There are a number of options based on the condition of your paint.
Always start with the least aggressive method and always do test spot(s) until you achieve the desired results.
IMO, jumping straight to FG 400 is pretty aggressive.
I'd start with PF 2500 on a green or white CCS pad. It's a great one-stepper!
If that doesn't work for you, try a second application before moving down to SI 1500 and then finally FG 400.
As far as the difference between SF 4000 and SF 4500 goes, 4500 is a finer polish and is primarily used for jeweling.
I recently switched from denim pads to damp sanding for my orange peel removal project and have been using Menzerna products on my PE-14 rotary to polish out the paint after initially cutting it with Meg's M100 on a wool pad. After using a variety of different pads and speeds I finally hit the jackpot with the following (all pads are CCS pads):
Step 1:
SI 1500 on a Orange pad at 1200 rpm
Step 2:
SF 4000 on a White pad at 1500 rpm
Step 3 (jeweling - optional):
SF 4500 on a Blue, Red, or Gold pad at 600 rpm (briefly 1500 rpm at the start to break down the polish)
Those speeds sound high and the pads may seem aggressive, but on my Honda paint it made a night and day difference in both clarity and gloss over softer pads and slower speeds.
Keep in mind that the exact process I used on my black Honda may not work on your Jeep. This was simply meant to be one example of the many different ways Menzerna products can be used together.
If its okay with the mods, I can post a link to a Camaro forum where Todd Helme from ACC posted an awesome article with charts on the different Menzerna products and LC pad combinations. VERY informative!!