About grain in film....
I wouldn't be too concerned with grain because even with 35mm Tri-X 400 enlarged to 11x14 (I do this routinely), grain is not obtrusive. Even though the name is the same, Tri-X of today is not the same "stuff" as we had several decades ago. Tmax 400 is about as fine grained as traditional ASA 100 film. This is just by developing with D-76 in standard way. No tricks necessary. If you are thinking (if you are in my age group) of old film, you will be pleasantly surprised. With high speed shutter available in 35mm gear, I pretty much have standardized on Tmax 400 and Tri-X film.
Yes, you can use flash... why not?
About developers... I started with XTOL and settled with D-76. It just works and to be honest, I really don't see much difference in results. When I started, I studied and reviewed lots of technical data and picked the "best." I wouldn't stress over technical merit of each developer.