if you are still weighing the pros and cons, I put another vote for 8x10 or 7x9.5. I just bought the most affordable basics, a russian wooden camera, some barrel lenses, a shutter and one shuttered wide angle lens with slight scratches. all this wasn't 500$ yet. I only have 2 double holders, but I'm looking for more if I see a bargain. it's real fun already. and it's so different from smaller formats.
I mainly shoot 120 film. when most professionals moved to digital and their old gear became out of fashion, I bought myself a 4x5 technikardan. it was great to explore it, but enlargers are really really expensive. and in the end, most of my prints are 7x9.5 or 8x10. so the difference between a 120 and a 4x5 negative isn't that impressing at this size.
all I can say is that a direct print from 7x9.5 has something special, maybe it's not rational even, but I just adore it. this is my very personal opinion of course. I just wanted to let you know.
In my part of the world, SF Bay area, you can't give enlargers away. My MXT is staying but go to Craig's list and you'll see 4x5 enlargers for a song. Getting a decent 150mm lens might take you awhile longer.