One way around the button on the sleeve problem is
step 1) take the button off, and stitch the button ON TOP of the buttonhole.
2) stitch a 1/2" of 1/4" elastic to one end where the button was originally stitched, the other to the back of the button hole (inside of the cuff).
Your hand is able to slide through the cuff now, but it appears closed, to the eye.
You can make your dress shirt a pull-on by keeping the bottom 4 buttons done up and using velcro on the top 3 buttons, again stitching the button on top of the buttonhole, and cheating the velcro underneath. Regarding the collar of the shirt....this is the challenge. A slightly larger button, with a shank of elastic stitched to it, attached it to the shirt,where the button originally was, should make it more accessible. It can still hide neatly behind a tie.
We use this trick for quick changes in the theatre.
Re dress pants: Most pants for Parkinsons seem to like elastic waistbands and drawstrings. My thought is, that you could get a tailor to cut the front of your suit pants as you would traditionally, but explain that you need the back of the pant cut with an elasticized waist. This will give you enough room to get them down fast. The other thing you might ask him to employ is a " pant hook" rather than button on the waistband. This is about 1" long and flat. Ask him to give you a discreet tab at the waistband front to help you pull the hook open. Consider 3 velcro 1" squares instead of a zipper in the fly.
Hope this helps,