4. I wouldn't recommend your irimi with the body to a 50kg woman against a big guy like you. Aikido isn't just a budo for big guys. It's for anyone.
5. I don't agree about the place to occupy in irimi. You think that we should take the space the opponent is trying to occupy. Not in aikido we don't. We let the opponent take the space they want. What we do is give them no choice. So that they want to take the space that we want them to take.
Niall, with respect, addressing #4 :this very short and....ok think metric! 55 kg woman always entered directly as a young woman with no m.a. training doing street patrol and concert security and it stood me in good stead. In aikido I had to be taught to go offline and to this day remain closer to centerline than many training partners expect.
re #5 I would say in my relatively limited experience it seems to me that in practice most teachers will teach and demonstrate both approaches so I wonder if it is truly philosophical or more either tradition or tactics or both. For example the most common responses I've seen as standard to shomenuchi for ikkyo is very much entering under the sword to occupy where uke is wanting to be. The few instructors I've seen who allow the shomenuchi to come to full fruition stand out by their rarity. Meanwhile in most of those dojos that agree on not allowing shomenuchi to fully manifest it is very common to allow a tsuki to do so while nage gets offline and a yokomenuchi may receive either treatment depending on what technique nage is supposed to do (enter directly into attack for gokyo vs let attack fully manifest for shihonage).
My two cents. Maybe worth less in today's economy!