I would go with about 2" then if you want to keep the buildup to a minimum. 3" starts to require things like brake lines, shocks, track bars control arms etc.
Cheapest way will be to grab a bunch of coil spring isolators from junkyard XJs (the alternative being some poly spacers), and then find some Chevy fullsize truck drop shackles (which are a bit longer than stock MJ) or find a used XJ 3" AAL (which would give 1.5-2" of lift in an MJ).