I am going through this now, even though I bought '07 100-series back in May. It had 189k mi, so I did the TB/WP 1st thing. Just spent $1,000 on other maintenance (incl replacing the blower motor that was too noisy due to bumps & knocks on a trail drive int he Serra Nevada mountains). I'm still finalizing my build but based on what I learned ...
Agree with the earlier comment: armor & recovery. If you're going to do trails or any off roading with rocks, get a pair of sliders to replace the running boards. Skid plating is also important, even more so if you tackle rocky desert stuff. And ( I read here) it improves your gas mileage.
Replace the front bumper with one that supports a winch (unless, you know you always go with friends / 4WD club members you know will have you covered). Bull-bar and Sierra bar are fine, but get the winch sooner rather than alter.
The rear bumper depends on your tire selection. The 275/70/18's should fit in the spare for carrying the spare (if a bit snug). My 100 had an aftermarket trailer hitch, which took up 2-inches of space where the share goes. Fine for the stock 275/60's, but I can't fit a larger tire there. So I have to replace my bumper with one that has an integrated tow hitch receiver and, to be safe, will carry the spare. READ THE FINE PRINT: lots of replacement bumpers with tow hitch received where the manufacture specifically says that bumper is not designed for towing.
So I'm getting the rear bumper that holds the spare. I'm basically choosing between the ARB and Dissent Offroad (although Slee has one too), and the biggest factor may just be lead time.
Once I know I can hold the spare, I am planning on 275/70's too ... ~2 1/2 in larger than stock, getting at least another inch for the axle. I am interested in 295/70/18's but after reading an exhaustive thread (here), I plan to go through this set of 275/70's then replace the wheels with 16" and move to a fatter, thicker tire like a 315/75/16.