I'll shed some knowledge(or my experience/opinion, because I'm sure people can disagree or say I'm wrong) on lifts for ya. A 2 inch lift has very minimal effects on your stock suspension components and everything else affected by lifting the body and frame. You really won't need to replace anything, though your stock shocks will limit downtravel of the axle and tire, and bumpstop extensions would be good if you need to limit up travel( if your larger tires are rubbing or in your case you have spacers and the spring can be damaged from over compressing it). If you wanted to stick with 2 inch I would just replace the coils and take the spacers out.
At 3 inches of lift longer shocks become almost mandatory. The track bar will be at an increased angle and will push the axle off center to a point that is almost noticeable and control arms will bind slightly. An adjustable trac bar would be a good thing to invest in, but the stock one can be used without too much trouble, as long as your not replacing the control arms. The stock control arms will work fine. you should be ok with driveline angles but you may experience vibrations in the rear driveshaft, and it's a good idea to plan on either a transfer case drop, motor mount lift, or a slip home eliminator and cv drive shaft. Your brake lines should be fine mine were good with 3 inches but it wouldn't hurt to relocate the brackets to allow a little more length. They have kits for this or you can DIY. Pretty easy and cheap. And longer away bar links are must.
4 inches of lift is stepping it up to a whole new level, at least cost wise. Besides shocks and coils, you'll really want to get adjustable trac bars, new lower control arms to prevent them binding with the bracket, adjustable upper control arms to dial in pinion angle and to adjust for pinion angle in the rear if you get a SYE, brake line extensions or longer brake lines, sway bar links or quick disconnects, and some people get away with a tcase drop but a SYE is the best way to go. There are a shit ton of 4 inch kits out there. Most of them are the basic and only include lower control arms and trac bar brackets and skimp on everything. I've heard of so many people unhappy with the ones like this that I would be careful and not just buy the cheapest one. But if you want a 4 inch lift do what your budget allows. And don't think about lifting any higher than that without a descent understanding of suspension geometry. Lol