Hi Wings. Reading the thread and your progress so far, I thought the following hopefully supportive comments and suggestions may perhaps prove of interest to you.

Congratulations on the choice of SIG's Four Star 40 kit. You've chosen arguably the perfect progression for the more confident R/C pilot who is comfortable and competent with the LT, and ready to progress to the next phase of the learning curve. The LT is itself arguably the perfect trainer and was an ideal choice for your first aircraft. So that you can better appeciate where my perspective is coming from, I freely admit to a bias or prejudice as having given considerable thought to it, my own choice for a trainer and subsequent progression some years ago was LT-40 to Four Star 40, both from kits. Albeit not the only choice, it was a solid and one I would repeat without hesitation. These days my personal preference is for sport pattern models, though I still very much enjoy my Four Star 40 and similar sports flyer models.

Adressing some of your concerns.

The Four Star 40 is an easy flyer and great first taildragger with no mentionworthy vices save a characteristic it shares with the LT in that it will float forever if you carry excessive speed on approach. You are already used to this from your LT so adapting to it with your Four Star shouldn't be an issue. The Four Star can safely be flown as slowly as the LT on approach. However, different from the LT it is highly aerobatic, much faster and nimble. An absolute delight to fly.

The Four Star 40 doesn't need much engine. Your current engine will do just fine. It is a small and very light model with a low wing loading. I've used a few different engines in mine and seen 'em fly with all manner of powerplants. The powerplant I found best matched of those I own (predominently two strokes) was my Super Tigre ST S40K which is very similar to an OS 40FX. I've tried grunty 45s (Enya CX) and 46s (OS FX), but frankly they are excessive power in this light airframe and personally I preferred and reinstalled the .40 mentioned. That said, the Four Star would fly OK even with a plain bearing low powered .40 such as the FP and is probably ideally powered by a four-stroke. I was tempted to put a .40 Surpass (my only four stroke) in another one and from what I've seen of those powered by Surpass .52s and Enya .53s, the power of even a .40 Surpass et al would be adequate.

Build it as per plan except perhaps giving thought to the the following considerations. Beefing up the tailwheel by lashing out on a DuBro tailwheel bracket and mounting it on a ply plate glued to the bottom of the fuselage will offer greater longevity. You don't need or want to fiddle with altering the dihedral or beefing up the supplied ply wing joiner plate. The full span ailerons are quite large and powerful. With wear, do watch for flex in operation around the aileron joiner. From my own experience, I would recommend reinforcing this area with a light layer of glass and epoxy and ensuring deep penetration of the joiner into the aileron itself. Insofar as mods go. That's it. At this stage of your R/C experience and with this model I suggest you forget the idea of cowling it. Keep it simple. If you decide you want a cowled model buy one. It's a less painless way of discovering how much of an infernal nuisance cowls can be even though they do look good. Pertinent to others suggestions of it not rolling or snapping fast enough, my only comment is that if a faster rolling and snapping model is desired, it is smarter to buy a Sukhoi or CAP, or if something which flys like an arrow is desired, buy a patternish ship. You already appreciate this I'm sure, but I mention it in passing. Speaking plainly, the Four Star 40 default OOTB is the right design for you now. As it stands, there's nothing shabby about the Four Star's rolling performance in its class and you won't be disappointed with either your expectations of its performance or the progression.

If its not in the air already, I can see from your progress that it won't be long. Set up and trim her true pre-flight, relax and confidently enjoy your test flight. You are gonna' love this bird. Like SIG's Four Star 60 and Astro Hog, the design is pure sport flying magic.