Inlines are certainly a different breed, however they are still a muzzleloader and share most dynamics.
I have a caplock in .50 cal that has a 1:48" twist. Because of this I can't shoot too long of a bullet. However my rifle does extremely well at 50 yds (the furthest I tried so far) with a 320 grn conical boolit. This isn't that short.
To begin with you'll need to know the twist rate. The faster it is the longer the bullet it will stabilize.
Quite frankly each muzzleloader has sweet spots as far as powder charges and granulation sizes go. You can't tailor your load using pellets. You get 100 or 150 grn charges. Mine, with that bullet, does well with 70 grns of 3F.
You'd likey do better and spend less by using loose powder. You can buy plastic speed powders with measured powder charges for ease and speed, which wouldn't be much slower than using pellets and no chance of them breaking.
Often people complain about pellets performing poorly the next year, along with some substitute powders. Real black powder never goes bad and can be dried out if it gets wet.
BlackHorn 209 is said to be an excellent powder. Triple 7 is rather good but also gets complaints about going south over time (opened container). Some, including me, drop dessecant packs in there. Maybe it helps and maybe it doesn't but it doesn't hurt to try. But I haven't shot anything in two years as I'm no longer close to an outdoor range.
You don't need an expensive wiz bang bullet. Try Hornady XTPs in both .44 and .45 cal. Even the sabots can change performance so try a few different ones.
120 yds max is not that far really. No need for a heavy powder charge or super aerodynamic projectile. A patched .490" ball can easily do that distance as long as the breeze is light and you've practiced enough and know the distance pretty well, and that's using my 70 grn charge of 3F Triple 7 or Olde Eynsford black powder. And that ball will go clean through on a broadside shot.
Ultimately you'll not know anything until you try some things. Personally I'd start with loose powder in 3F (it burns cleaner and produces a slightly higher velocity compared to 2F) and begin with 70 grns of (by volume) powder and a bullet. Shoot 3-5 shots and see what you get. It might be best to wipe between each shot. Then try an additional 10 grns all the way up to the max rated charge of 3F powder. Keep good records and then start over with a different sabot.
Take an appropriate cleaning solution to swab your bore. Plain water works for black powder and Triple 7. I use one patch (both sides) followed by another patch (both sides) with rubbing alcohol with helps evaporate the water. Give it a minute before loading again.
I've never used sabots, and the only substitute powders I've used were Pyrodex P and RS, and 3F Triple 7. My experience is quite limited. And my rifling has deeper grooves meant for a patched ball, but one day I'll try sabots and my cast lead bullets just to see.
Oh, as for bullets I'd try anything in .44/.45 from 240-300 grns and meant for hunting. Hornady, Speer, Sierra...
