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I've done a few comps on the PBC but only chicken. Did fairly well too and beat some well-regarded teams too. What worked was not doing the butter bath in a pan that most other teams do but just grilling direct over the coals on the grate with both rods out. This gets me about 350* with good appearance as the meat is high enough over the coals to not get burnt. Got bite-thru skin too but I do use meat glue.
Ribs turn out great and you can get 8 racks hanging but I'd worry about wrapping that many and putting back in the PBC on the grate (we do Johnny Trigg style ribs with a few twists). 3-4 racks cooking and then wrapped is perfect.
As for butts and brisket, I've only done a few practice cooks on the PBC as we use my partner's stick burner for that. For brisket, you're gonna have to trim it down a few inches to make sure the packer is a couple of inches off the coals. For butts, I really see no benefit in hanging vs grate as the magic of hanging comes in from the side profile of your meat getting heated vs a more direct exposure horizontally (on the review of the PBC on amazing ribs website, the physics expert gives a good explanation for this). So, I cook butts on the grate and hang the brisket if I can.
If I was going to do a comp using all PBCs, I'd want at least 3. Ideally though, I'd get a Gateway drum or BPS drum and pair that with a PBC for capacity purposes as those are much bigger. Just my opinion.
