I think from your explanation and the replies you are discussing Shomen Uchi Ikkyo Omote tachi waza.
I just want to preface my comment with that as we are taught different movements depending on the attack and waza. Example our Ikkyo is way different if its Shomen Uchi Ikkyo in Hanmi Handachi Waza vs. Tachi Waza.
Our basic instruction is to irimi direct towards Uke as he strikes with timing such that we catch the elbow on the way up with our back hand and front hand.
We continue to move into Uke as we move his arm in a vertical circle and move his elbow towards his face(much like a lot of other replies).
As we attain the point where we have taken ukes center/balance we start to cut down his arm without grabbing it with the front hand. The power is coming from our center and is transmitted through our hands.
We have been told to be careful not to pull the arm and hence ukes center to much back into us but rather stop around the knee. By this time ukes shoulder should be lower than his elbow.
The straight down movement vs. sideways one are both used by us. I have been told its a case of how well we do the technique and if uke manages to resist the final down motion.
If we can apply Ikkyo well enough the ideal is one motion straight down to the ground. If uke manages to catch himself at the point where he is turned around and maybe on his knees and resists then a change in direction to the side may be needed.
Once uke is on the ground we pin with approx a 90 degree angle and with the back of uke hand on the mat. The idea of using our tegatana around the elbow may be done or even just a settling of our weight as a hold down.
Something interesting I was told once was to be careful not to place the arm at to high an angle towards ukes head as while it may be painful it can be easier to worm out of by a tough uke.
I like the knee against the ribs thing too.
The Hanmi Handachi version is similar to your 4 & 5 combined. Recieve the attack, give a little and rather than turn it back toward him just drop the arm straight down.
Gosh this is hard to describe. What a good excersize. Better not tell my teacher or he may start making us write out description as part of our tests.
All the best