Hey, welcome to your already-found addiction, and now to CB.com as well!
Sounds like you're off to a good start. Here's my take on what you're asking:
Trying to preserve the original drive character of the vehicle, with subtle improvements.
Easy to do with what you're planning, and even making it better.
Specifically I am looking at a 2.5 inch lift to improve stance, capability, and allow 30 or 31 LT’s.
You can do most of that stock, so the idea of 2.5" of lift will put you in what I think is the sweet spot for an EB. Both in looks and handling/ride comfort.
Anybody ever experience compromises going from stock to 2.5 inch/11 leaf set-up? Looks to be an easy step.
It is easy, but yes you can experience some compromises. Any time you lift an EB you're going to change the steering geometry in a negative manner. How you like it is up to your individual tastes though. Many here don't make any corrections and find that it steers and handles just fine. While others don't like it and end up with the usual corrections of dropped pitman arms, trackbar brackets, adjustable draglinks and the like.
Progressive rate springs look like a good answer up front.
They are. Some still like the linear rate, and companies like BC sell that style and users like them. I personally prefer (even before I worked at WH) the variable rates and have been running them at different heights for more than 30 years.
Is it worth the trip to go with the long travel shock tower? (Basically WH system #3 vs system #16)
No. Unless you need or really want them that is. Are they cool and do they work as advertised? Definitely. Do most of us need them? Definitely not.
Describe again just exactly what you plan to do with your Bronco, and we can offer better advice in that department. But for 90% of new owners, save your money.
And don't tell Jim I said that!
Duff vs. Wild Horses? Anybody have a bad experience with either kit?
Again, nope? I don't think so anyway. Hard to go wrong with either. They are both slightly different, and both companies approach certain details differently, but both are high quality and both companies stand behind their products.
I've known the Duffs for going on 30 years too, and have worked at WH for almost 6 now I think? (time goes by so fast!) but most of us offer pretty good stuff. I like ours of course, but plenty of forum members here will tell you that ours and the Duff suspension products are good stuff.
How much tire can I get under the uncut EB with a 2.5” and NO body lift? 30x9.5 seems to be a no-brainer, but I hear people talk about a 31X9.5 (but I can’t find the tire size anywhere).
There are more 31x10.50's these days I think. The old 9.50's are like hen's teeth, but I do believe that there are still some out there.
And yes, you can fit some amazing things under EB's if you use the right backspacing on the right wheels. Nothing is more important when fitting these otherwise modest sized tires under that rear fender.
Can I get away with stock brake lines, e-brake, and driveshafts when going stock to 2.5 inches? I hear different things.
That's because every EB is different. Period. And every EB owner is different too.
You hear different answers because different owners approach their mods in different ways, and often achieve different results. Even if Broncos weren't different, the owners successes would still be!
For 2.5" of lift you can get away with stock on all counts you listed. However, the two soft brake lines to the axles "should" be part of the changes you make, especially if you're replacing the old ones anyway.
If you're not going off road and the biggest bump you're going to hit is a speed bump in a parking lot, then the stock lines are actually long enough. But my feeling is don't compromise in the area of brakes, so as soon as you think you need to replace lines, or if you plan any off-roading (even mild stuff) then always err to the side of caution and choose the longer version for lifts.
Your driveshafts don't need to be changed. If they do, you likely did something wrong.
The e-brake cables are more than long enough for up to 3.5" of lift with no off-roading. As soon as you start comparing wheel travel numbers with your fellow Eb'ers or Jeepers, get the longer cables because the stock ones WILL BE your limiting factor. They still work, to be sure. But they're shorter than optimum.
Best of luck! I know you'll get lots of good folks around here giving you good answers. Glad you're checking first though, rather than after the fact.
Paul