Choosing a film camera for the future... (35mm vs 4x5!)

Excuse me if I sound blunt, but you seem to put the cart before the oxen. I.e. the opportunity (of buying one of your deceased friend's cameras) triggering the desire. Better would be if you would state something like: "I've always wanted to shoot Large Format, even had a short experience with a loaned camera...". Or same with 35mm film... In other words, a pre-existing, well-defined desire for a certain photographic practice, being met by an opportunity to materialize.

But you haven't even decided between 35mm and LF. And what about the various flavors of MF, slower paced than 35mm, but more practical than 4x5"? As an example, taking into account one of your stated goals, religious architecture, what about a 2x3" technical camera with a rollfilm back? IMO, you should firm up your preferences; analyze what each option means end-to-end: how many pounds of equipment am I ready to carry, how far, how often? how will the films be processed? by myslef? by a lab, at what cost? how will they end as images? on a computer screen? on a wall? Borrow or rent the relevant equipment. And only then find out what is available; if something close enough happens to be in your friend's estate, good for you.