Congratulations

I really like handgun caliber lever actions. I have quite a few in 22LR, 357 Magnum, 41 Magnum and 45 LC

I agree on the top end just use what works in our revolvers.

H110 is a great powder for long barrels. My 357 magnum handgun loads really move out in the lever gun
My 125JHPs which chrono at 1300+ from a snubby model 27, 1600 from the 8" Python, get to just under 2200 in the 1892 lever action rifle

The 158s hit 1200, 1400, 1750 respectively

My 180s are not that fast since I loaded them to be sub-sonic, not full power, in the lever action.
They get shot in a lever gun that I have threaded for a suppressor

One of the really cool things that can be done with a handgun caliber lever gun is the development of a cat sneeze load. Paco Kelly did an article about this 20+ years ago.

Using pure lead balls and small powder charges of fast powder you work up a slow load that still clears your barrel. The result is an almost silent load, it is as quiet as a cat sneeze so it is hearing safe

My 45LC load puts 2 .458 diameter balls into an inch of each other at 20 yards. Those weigh 140 grains each and move out at roughly 600 FPS. It like a double tap from a 38 special snub but at distance.

I never worked one up for the 357 since I had the 45LC first.