Buster Crit Team

Yea those will do the job just fine. Only possible upgrade for star gen is Jack from the ones you already have. For support, Hans fills in for now but for now the best support would probably be waver followed by Nightingale as buster support. Waver's +50% crit damage for 3 turns buff is op plus he's waver. Hans is the mini waver but his crit buff is only for one turn. He does make up for it though by buffing crit gen rate (maybe) and by generating his own stars but if you want to seriously use him think of grailing him to 80 at least for his own survivability and upgrade all his talents. A 10/10/10 level 80 Hans is a mini monster

jUsT rOlL fOr mErLIn

You can, but it won't be all that great. Gil and Ozy are both good dps, hans is good crit support. However, fuuma, while being the best star generator you have, cannot generate them passively. He is also a quick servant, so you'd have one arts servant, one quick and one buster on the same team. There won't be too much card synergy but it's still workable.

Honestly speaking Gil is almost a one man buster crit team having strong passive buffs, high hit counts that can provide him stars, and a massive attack stat so you can put him with anything here and call it a buster crit team if you want. If you want to be a bit more optimal Gil, Hans, support Waver is a very solid setup.

For Ozzy he has a bit worse self star gen(though makes up for it with better self sustain and non crit damage) so for him I'd say Fuuma and support waver with Hans in the first back line slot would be a more efficient comp.

In both cases Ozzy and GIl are both plenty strong by themselves and will do fine regardless of the composition.

If you have a 2030, put it on Hans and grab another Hans from support list with a 2030 (you can always ask for these kinds of people in facebook groups or anywhere like that). This would work with any critter whether it be buster, arts or quick tbh. Just note that berserkers and avengers that don't have star absorb may not be the best option as the crit hitter in this composition

Other than Gil and Ozy that you mentioned, this can also work for
Tesla
Amakusa
Karna
Drake
And various other buster critters (since this seems to be your preference)

If you don't have 2030, the Iskandar CE from accel zero event is also good

I was wondering about this as well. I have a similar setup, with a Herc Ozy (Both 80) and Rama (60) to utilise the stars. Kerry or Cursed Hassan for the star gen and Hans as the support. I can grab a support Waver if Hans doesn't suffice.