For tire size here's a good starting point, courtesy of our own Nwoods
https://lr3tips.wordpress.com/2007/03/14/46/
I personally run a 275/65-18 now and plan to change to 275/70-18 this fall. YES, I HAD TO MOD TO FIT. If you're adverse to cutting on your truck, stay to 31.5" diameter or less. You may have a tiny bit of rubbing with a 265/65-18 but it shouldn't be an issue and is easily dealt with if it bothers you.
Tires are like religion or politics...so many personal preferences based on so many variables. In general any good AT tire should be good for you. You will want to look for a tire with sufficient load rating. While many of us with built-up rigs run E rated tires this won't be necessary for a more stock truck like you're planning. D should be fine. For specific recommendations it will be best to talk with some local guys to get a feel for what they like in your terrain. I happen to be running Goodyear Duratracs right now and they're great in snow/wet and good everywhere else but not strong enough in the rocks - and I like to pretend I'm a rock crawler so I'm going to something tougher and more aggressive next time. If you haven't read it already, here's a good starting point for AT tires:
http://expeditionportal.com/where-the-rubber-meets-the-road/
I do have a roof rack, an Urban Offroad Exodus Series Platform Full (wow that's a mouthful). I picked it as he's based in CA as am I so shipping was easier but mostly because I wanted a very low profile rack. The Frontrunner you're looking at is a very nice piece and also very low profile plus they have many accessories for it should you want them. I however preferred a more traditional tubular look instead of the more high-tech aluminum look of the Frontrunner.
I don't think you'll need a jerry can. I do have one, as well as a spare tire mount, on a custom built rear bumper. But again, horses for courses - I've been known to drag that big 'ol but off rock ledges so a welded on steel bumper was high on my list as was getting the spare tire out from under the truck and having room for a larger spare. And here in the west we have more long trails where you can go days without a fuel stop. Heck, for our OR Back Country Discovery Route trip earlier this year I had my jerry can full plus another 3 gallons on the roof rack in the form of a small outboard motor tank strapped down. I used nearly all of it too. FWIW, if you do end up running some trails that will need extra fuel I think the outboard motor tank on the rack is about the cheapest/easiest way to go. You can pick one up used in 3 to 6 gallons from craigslist pretty cheaply and get a super-syphon to transfer fuel without having to make a mess.
RTT vs Ground tent is another big debate. I ended up going with an Oztent RV4 myself - picked it up at Overland Expo west last year as a demo model and I've put quite a few nights in it since from 15* to 90*. It's big and heavy and expensive though, so while I like it I don't know that I'd recommend it as your first tent. You might want to consider something a bit less heavy to start with, but do look at a decent product. People here like to bash them but if you have an REI in your area they offer a pretty good selection of tents and the staff are generally knowledgeable and helpful. Heck, they've let me set up a tent I was interested in right in the store. My 'lightweight' car-camping tent is an REI Hobitat though I think it has been discontinued now. I personally like the idea of a RTT for quick up/down, but don't like the mass up high, having to go up/down the ladder, and lack of standing headroom. Not to mention I'd probably damage it by leaning into a tree or rock.
I'll second (third?) what others have said about Optima batteries. Once good, now questionable. Odyssey, Trojan, Lifeline are all brands I like. Of note, the Sears Diehard Platinum marine AGM batteries are Odysseys re-badged. I think the stock size is a group 94, but there are options for fitting a bigger battery. Although if you go with a dual battery setup I would just keep the original size in the stock location.
One other thing worth having is a portable compressor to inflate your tires. You'll find you're changing your tire pressures regularly when off road vs on road and a way to re-inflate tires is really useful. I used to run a Viair 400C (still have it) and was happy with it but more recently went with onboard air using a Viair dual 300C system under the hood. While not super fast, the basic MV50 compressor is a very inexpensive and popular option. Less than $60 on Amazon. While your at it, a good tire plug kit would be a good thing to have on hand too.
Ignorance is bliss until you push it onto someone else. Everyone knows about coolers and ice. I offer up ideas that someone may not have come with as obviously so that they might choose what works best for their own purposes.
