CW once put together a BW only leg program, and posted it as a reply one of the forums, either building a better body, or Strenght I can’t seem to remember. But it is worth hunting down if body wieght exercises are all you are capable of doing.
Also I agree that 400 pushups are a lot to hit in one session, and your time may be better spent doing some type of total body, or upper body lower body split. maybe like
M,W,F: total body
t,thurs,sat: cardio/esw. (if ok with your Doc)
Mon, Thurs= upper body: both pushing, and pulling.
Tues, Fri= lower body: both quad, and hip dominate.
Weds, and sat could be used to do some type of cardio/esw work, and sunday would be your off day
I also agree that you should look into adding as much core work, as you can handle and throw it in were you see fit.
Oh, and I will look around to see if I still have the link to the CW program I mentioned above.