1 - I've heard that when entering the States, he should come with me to the USC line, and when coming back I should go with him through the UKC/EUCitizen line. Is this true? (I know all airports are different)
It seems to vary from airport to airport which line they want you in, but I'm generally fine wherever. I often go to whichever is shortest and let them sort us out and just put whichever passport applies to that queue on the top of the pile of passports. Now and again, they will need a different stamp than they have at the counter and they may move you over to someone who has that stamp. There used to be formal guidance on this here on UKY, but it still seems to sometimes be handled differently in different places or days. You should be fine though. Don't stress.
2 - We are flying out of Norwich through Amsterdam and coming back the same. Since I'm here on a spousal visa and my page will not be stamped coming back into Norwich, should I just keep all of my flight information of when I re-entered the UK? I don't want to go for ILR or Citizenship and have them say that something's wrong due to the no stamp from Norwich.
My passport usually is stamped coming in (even within the EU), since I have a non-EU passport, but if it isn't, it isn't the end of the world. I don't think it matters tonnes as you'll be showing your proof of living here through utility bills and such, which you wouldn't have if you hadn't returned.
Having said all that, the few times that it looked like they weren't going to stamp my passport at passport control coming from EU countries, I've just asked the IO "I'm working towards ILR, do you mind stamping it so I have evidence of when I came and left?" I've never had trouble getting the stamp when I asked for it. I think you're thinking of the posts from people talking about concerns about coming through Ireland on your first visa when you do need a UK stamp. There are no concerns with coming in once you have the visa. You are free to travel just like anyone who lives here.
3 - Can I bring back home-canned jelly? Especially some of my speciality grape jelly. It's all labelled and sealed but I'm not 100% sure on the rules.
Think so, I've not had trouble with stuff like that. I never feel like it's uber clear, but I don't think there's any problem with jams and jellies. It's mainly meats, fruits and vegetables that are troublesome.