I strongly recommend that you read Don Parker's (sorry, Capen,Dobbins & Parker) book on observing and photographing the solar system. Autors are (were) among leading planetary observers and imagers of our times, and they certainly have some weight behind the advices given in the book. A plane window is an excellent idea, but it might easily cost SEVERAL times the price of a good mirror. Its main advantage is escaping the problem of tube currents (spider effects are NOT that much of a problem for planetary observatons). Not sure about the Nitrogen idea, though. I think that much more experienced people failed at that (Couder?).
Bottom line - it is better to have a GOOD, SIMPLE and LARGE telescope (Newtonian) that will work well every time the seeing allows, instead of complicated, difficult to execute and operate design which NEVER delivers. Just ask Don Parker (or pros at Macdonald or Pic du Midi).
Bratislav