DH

A lot or none-depends on what you're doing. I have met any number of ICMA people who practice Solo under master class teachers and had nothing. So how many got it...who knows?

See below

2) What role, if any, does auxillary western-based strength training play in the development of the "actualized IP practitioner"?

Nope!! Not even close.
I think you're confused by what you heard about me. I am only 6' about 218 lb. I am no "physical beast" by any measure.
Now, one of my guys, Andy is 6' 3," and about 260lb. He is extremely soft and a good jujutsu player. He IS a physical beast and when turned loose...quite interesting tp play with, and probably one of the nicest guys you'd ever want to meet.
To answer you about western lifting and IP/aiki
I can tell you that every time of my guys used to go do a six or eight week lifting cycle-their usable power went down, not up and I could "catch them" far easier when grappling. Over a month or so, they'd softened up. Some went back to normal, others it took a long time. It was NOT a better way to go, but young men being vein.....

3) What role does tension play in the development of IP?
For me...none.
Now, pressure applied? Training against tension?
Tremendously useful.

I don't advocate tension in IP/ aiki training. I have felt/seen and had explained in detail some of the tension ideas; some have talked about it as "tension to identify paths first-then soften later" others as a form of "whole body tension" mostly just using the back line (which is limited), and still others count on using a type of relaxed musculature around the bones as the hard frame and work from there. With most of the former you see the use of the hips and same side power, on the whole they make a fairly stable fighter but it is one who has a body type that can be "read" pretty easy and most of the typical moves in TMA are meant to be used against that type of body use. I see it as typical movement-just made stronger. There are people offering exercises I have seen and had explained to me that are like that; the back line is stressed, with hips and shoulders aligned and explained as such, the "same-side-weight" trained as such and laid out; both on video and in the online hand- out fliers from seminars. I had tried a few and quickly dumped them as I didn't like what they were doing to my body. Power is not all the same. I'm not saying better or worse mind you, just that I have personal goals and uses in mind. And while that type of movement can be strong, I wouldn't personally choose to train that way for many reasons- and in particular for weapons and freestyle.

There are particular reasons why certain classical weapons training morphs into empty hand so well and can be powerful if you understand it. Earlier discussions and comparisons with various Koryu I did with Ellis has led to some interesting and revelatory observations on Koryu movement. Most of the good Koryu people do not move the way I outlined in the previous paragraph. Their training has demonstrated that you can't really use long weapons well that way. Most Koryu use a body movement that is quite different and would not generate power in that same-side-weight, one-line hip generated way that you see so often in modern adepts. You can get stuck and not be free enough for moving the weapons and yourself. What is even more interesting is to see more and more of the Japanese teachers now mucking it up, and just about all of the westerners. They don't move like their master class teachers-and they are at a loss to understand why. Further research that Ellis doing is supporting the position that there are more and more power building and solo drills that were -for the most part- discarded. Even with modern adapts acknowledging that some of the old guys were powerful…sound familiar? Next we can get into the idea of projection, and precursers to movement and some rather heady stuff-all in Japanese Koryu.

Anyway, there are many methods out there. And I'm sure everyone of them is pretty sure of what they are doing. Everyone has to make their own assessments. From western body training to Martial arts, to waza to principle based training, we can see there are ways to move that on the surface are powerful. They just are not all the same. Some are now stating that "center based training and movement" is all the same, that it must be. Yet I have heard very little to actually support that assertion.
So, yus pays your nickel and yus takes your chances.

There is simply no reason you have to train tension from the beginning. From the beginning you can train soft. Overall, I think soft-power trained for use in certain ways- wins. The problem is that training this way means you have to let go of perceived notions of power and "learned and burned" movement you are familiar with, and train something different.
I actually think most people should walk away and leave soft training alone. I even tell them so. They won't follow through anyway, and their bodies are going to get stuck in between they really won't do either thing well. If you are approaching it from the DR or Aikido side of things, than soft is best approach and breath-power training is key in doing so. It just so happens I developed a way to use that in freestyle fighting-a place where most TMA didn't go.

The best "connection" (not tension) is a stretchy feel and it happens slowly and is driven by intent based movement. There is a looseness you need to shoot for that later one will allow you to generate power and move without telegraphing. You might want to consider that the main three opposing forces you are training- are all joined by one common opposing force; expansion and contraction. Bear in mind that while intent driven movement has to be largely mental at first, it is most certainly physical later on, and will have increasingly real physical results in your body-you will feel it happening. Tension will just screw it up. Were you able to generate some simple intent-based movement you can experiment and satisfy your own questions; have someone push on your chest and then sink with intent while rising over him with intent. Then stop and start over by contracting muscle groups to do the same thing and see how far you can get with that. Then ask your buddy which one felt more powerful and is harder to "read."
There are other training drills to do to target the shoulders and hips to train them to loosen up and be part of a neutral conduit of power instead of a generator and sticking points. It's pointless to explain them here, you need hands on. I think training to target the hips and shoulders is a major goal for most TMA people. Japanese TMA are almost cookie cutter; move from the hip, use too much shoulder, one-line movement, and stiff-way too stiff. So there is a lot of work to do to soften up.

Don't misunderstand soft training. Most guys I have now met and trained with equate softness with evasion, and release. They had no concept of soft-(truly soft) being In-vasive and controlling. Moreover, their concepts are of single point use, a) soft evading or b) hard entry, occurring as one or the other-maybe in rapid succession but not together against two or three point attacks. Even when we discuss a different model, for them it still becomes a) soft evading b) soft enter. They still had no concept of how it worked together, and how to train it to work together in solo training.

Soft can feel soft and strange to many martial artists both with you absorbing force and generating it, but at times it is anything "but" soft to those putting force into you. Over time (depending on how you choose to train) you will gain a loose snapping center generating quality to your frame) this becomes extremely beneficial in changing forces coming into you or pulling on you. At any point in time you will be ghosty and generating power....at the same time, and at any one point of contact. Overal, they feel a pronounced lack of control when trying to screw with you
Over time your center becomes far more involved and active and the driver to do all sorts of things. It just takes time to change your body and the way it naturally moves. Most do not have the stomach for it and simply quit before the real changes take place.

I dunno if any of that helped.
I hope to hear -years from now- that you had gone out to meet many people with power and come back with opinions and observations of your own and how it affected your practice. There is probably going to be false starts, experimenting, discards, changes, on and on. Be tenacious, get obsessed, just don't stop.
Cheers
Dan