You can lower the front close to 3" and not hurt BJ's, I have over 100k miles on my BJ, since lowering.
For power beyond say 250RWHP, skip everything else until you find a way to get custom exhaust manifolds made. The existing choices are choking off power at the stock level(200), so going past 250 is like breathing through a straw. It needs bigger manifolds, much bigger than 1.5" pipes.
Find someone who can make log manifolds for it, that's the simplest way and actually not that hard for a good welder. Make the pipes 1.75" at least at the heads, and 2" or more where they join, and 2.5-3" at the collector area, located near the stock collectors. Then make the rest dual 2.5" or bigger all the way back, with two mufflers(not one).
Just such a big exhaust should be worth 30HP on a bone stock Explorer, after retuning the computer.
To change the cam takes removing the engine, the stock truck roller cam is very good until you upgrade the heads a good bit(TFS TW etc). Then the stock HO cam is very good until you are ready to go to a true custom cam.