Hold on, I went back and re-read.
First the OP wants to build a better camera than any yet-so-far ever made. Good luck!
Second, he says he doesn't know about 5x7 or larger lenses. I wonder if he has even used 4x5 yet? I'm betting he hasn't.
Third, he is in medical school... !?!
And fourth, he is tight on money. Any wonder?
While I am sure a $1200 90XL would be amazing, the sort of lens this guy needs is a $250 Schneider 120 Angulon or something in that ball-park. An inexpensive vintage wide-angle -- a simple tiny, slow 90 year old lens... seriously. They are usually quite sharp and have a wonderful rendering... I know the mindset is to shoot with the sharpest most-modern glass but you'll just end up compromising further down the workflow chain (mediocre scans render the $2000 lens pointless for example). So why not learn to adjust to mindset of making a good picture instead of owning bragging rights? Besides when the money kicks in, you could always trade up and mount the four-figure $$$$ Uber-lens, become bitterly disappointed with it and find out I was right ;-p
(It's up to you if you want to be messing around with camera design and building at all given the time and financial constraints of medical training. But my advice is to forget about reinventing the wheel and just buy something more modest and less than you can afford... then go out and enjoy shooting making the most of your limited resources and time.)