Hi there and welcome to EBN! You sound just like me before we got Rook last October.
We've talked about getting insurance but still haven't done so... and knock on wood... Rook has been a pretty healthy puppy so far.
Our breeder had Rook on Royal Canin when we brought him home, but as soon as I found EBN I realized how important a quality food was. We switched him over to Fromm Beef Fritatta around four or five months. He has been doing really well with it. Still some water eyes but I'm not sure if it might be a food or environmental allergy causing it. When he is a little older I want to do an allergy test and maybe figure that out. What works for one bully doesn't always work for another, so it might be trial an error for you to find the best one for Seamus.
We started Rook with a collar, but recently switched over the a harness. You would not believe how strong a little bulldog puppy can be, if Rook does pull on his leash I feel much safer with the harness than the collar pulling around his neck. And he actually walks much better now with the harness, so I think he likes it better too!
As for apartment potty training... I don't know how old Seamus will be when you bring him home, or if he will already have all his vaccinations. We also live in an apartment, but we didn't let him outside until he had all of his puppy vaccinations. Since we don't have our own private yard and there are countless people and animals walking passed we couldn't be sure the area outside our apartment would be clean and safe for him. We didn't want to risk him picking up parvo or anything else that he wasn't protected against. So for the first month it was all potty pads in the apartment for Rook, which he picked up on immediately. You will pick up on the things he will do to indicate he has to go... for instance, Rook smells around a lot before he poops. Just make sure he gets to the potty pad, and give treats and praise when he does it correctly. Once we got the all clear from the vet, we started going outside for potty breaks and never put down another potty pad because we wanted to make sure he understood going outside was the only option from then on. I was really worried about how he would do with this transition, but when we told him to "go potty" he did. We treated him and gave a lot of praise every time he went outside... nothing if he had an accident inside. The trick is to know he has to go before he does, and lots of trips outside just in case to eliminate any accidents inside.
Good luck! Can't wait to see pictures of your little guy when you get him!