i did the 4" RC lift on my 94 YJ. Its only my trail rig and not my DD. I don't get any vibes. The springs were a little stiff at first, but i trashed my trac bars and the ride is great compared to the shot stock springs that were on my rig before. You're going to get LOTS of opinions, but I haven't had any issues with the lift on or off road...yet
you def need an CV Driveshaft if you're going to do the SYE. I went with the TC drop that comes with the RC kit for a while which seemed to work out great, but the drive angles are pretty steep. I'll save you my story, but i ran into issues a few months after installing, which I blame on the angle of the DS. Every rig seems to have its slight differences, so you may be able to get away with a TC drop for a while. if you can afford the SYE i'd go for it. Chances are that you will be going that route in the future regardless.