DIY at home. Chemicals are cheap enough, last lot I bought was around 20 quid and I've developed around 15 or so films and not 'run out'. After a while it becomes a guessing game and you have to let the film sit in the chemicals for slightly longer but it's fairly easy to gauge. Recently invested in a bag and film/chem mixer - it's a bag with arms on (that go into the bag, if you like) and you have to fiddle around opening the film cartridge and spooling it into the mixer, but it saves me having to black out an entire room and then working with 3-4 buckets of chemicals and water in total darkness. The hardest bit is maintaining temperature in the chemicals. I'm developing more at the weekend, happy to take pics if you're genuinely interested.
Medium format is no problem, again I do it myself and use the same chemicals as for 35mm.
I have a Fuji GF670, lovely camera but a beast (although IMO not as unwieldily as some of the TLRs - I think
@indigolemon has a Seagull IIRC). Going on some of the Pentax kit I've used in the past I don't imagine you'll go wrong with a 67. 120 film is such a PITA though, really. Of all the stuff I have my favourite is my Minolta Hi-matic 7s, cheap as chips on eBay but the quality is way better than any other 35mm I have. None of that ISO either, ASA and DIN

(although as I understand it ISO = ASA).