I've been running the Rough Country progressive rate 2.5" springs with the OME N66 / N67 nitrocharger shocks. I like the combo. Not spungy but not harsh either. And the OME shocks valving works within the range of the progressive springs. Todate I've not had issues with sagging on the RC springs either and I've been running this combo for a number of years now after ditching my BB.
As to potential vibes. . . . 2 - 2.5" is about where they'll start showing up. The MML will help but you might get a little something. You can space the t-case skid down about 1/4" by stacking some washers between the frame and skid and you don't need to swap out to longer bolts. I did this with my BB back in the day and it helped. If you need to space more than 1/4" then you'll need longer bolts. Also, running a 1/2" spacer isn't the end of the day. It'll give you time to save up for a SYE / CV driveshaft if you want.
Also, something to keep in mind. . . if you're getting a SYV / CV driveshaft that means you'll need to get adjustable rear control arms. And it's not much extra effort to do a belly-up skid conversion. Just the cost of the skid plate at that point.
So, get your spring lift and new shocks. Space out the t-case skid if need be. That'll give you time to figure out if you want an SYE / CV set at all, if you want JUST the SYE / CV set up, or to do the full money belly-up conversion.