Anytime you go over 2.5" of lift you open yourself up to a myriad of other modifications needed to make that work. Most importantly, you'll need to swap out your driveshaft for something aftermarket.
Others will hopefully chime in with their experiences, but that's the first thing that comes to mind.
It's *possible*, sure, but not really advisable to stack lifts like that (especially with spacers).
Keep in mind that many of the 2.5" lift kits on the market provide 2.5" lift to Rubicons. If you're in anything other than a Rubicon, you're likely to get more lift out of them. For instance, the MOPAR 2" lift kit is known to provide closer to 3-4" on Sahara/Sport models. Similar with other 2.5" lift kits.
Also, as @rohdawg pointed out, going over ~2" of any sort of lift is going to introduce other things like steering and whatnot that will need to be stabilized.
The other factor to consider is that when you go more than ~2", your stock tires are going to look pretty silly - like your Jeep skipped leg day or something. There are TONS of threads showing what various tire sizes look with lifts, so do some browsing. If you go up from 33" to 35" tires, you introduce a host of other factors, too - tailgate hinge reinforcement, spare relocation kits, but also new wheels/spacers so you don't rub, and potentially, the need to regear (totally depending on what you currently have).