Welcome!!
285/70R17's should fit fine (or 285/75R16's depending on rim size)- these would be 33" tires . I have the 255/80R17's- (33.3" tires) (255/85R16's if needed) in the BFG KM2's and those work on almost any terrain and really wear well. They make them in the 285 size but cost more and at that time i was just looking for clearance and the "pizza cutters" did that well. They do look a litle strange without wheel spacers but do the trick (look like an old postal jeep).
As far as brand and style you will get a million different answers. All I can say is if you can get together with some other FJ owners, you should be able to ride in theirs and see what you like. I like loud mud tires (howling!), some like quite tires but want all terrain. Main thing to consider and most dont, is wear. You will spean a lot on tires and if there made only for mud and wear out in 10K- your out a lot of money. If you like quite tires stick with tread patterns that have the treads interlocked (connected) otherwise go with sepparated treads (blocks) and you will get more noise but better cleaning of the tread in mud. I dont play in the mud (like rocks better) so my tires are for climbing, but most are multi- purpose.
Otherwise with size comes the rub. Depending on which tire you choose, you may have to cut off you "ears"... The Body mount chop (known as the BMC here on the forum) is removing those two "bumps" that protrude into the wheel well behind the front tires (behind those plastic flaps). The body mounts are your biggest problem at that point but can be easily removed with a multitude of tools. Not that difficult- you just have to build up the want to cut parts off your truck. For me it was the fact that my 35's wouldnt fit and then they just got cut off. took me less than 5-10 minutes a side.
Best of luck to you and Semper Fi
:cheers: