I think your list of 'essentials' is good - however you need one more item which should probably be in the high end of the list: Allways move from your center. I know this is very similar to your item no. 4, but I think it's important to emphazise that your center should be the primary origin of movement.
In my experience both the timing and the size of tai sabaki should follow from the attack you are responding to thereby guiding your footwork, so it all comes down to being aware of (every) uke at all times and move from your center. Can't do it though - but I just LOVE practicing
Just my 2 x 0.01 Kr.