When I got the first .357, I was scared to death to ream it for the same reasons you're thinking. It was a shooter. When I got the second and it shot well too, I said "what the heck, risk it". Well after reaming, I couldn't see any difference in performance with .38s, mags or maxis. I believe the freebore is a non-issue. The .38s don't "bounce around" at all. They shoot accurately and a little high due to muzzle jump....lower velocity and longer time in the barrel. That's all.
I think ya need to relax until you get the rifle. You're dreaming up problems that in reality, more than likely don't exist. It may, perhaps, need some tinkering to improve accuracy (unlikely), but if it does, the how tos and help are right here.
Yeah, max brass costs, but it's only pennys more to reload over .38s once you've got it.
There's a lot of mis/disinformation on the web about Handis......the facts reside here. The pros, the cons and the cures. Search .357s here, and you'll find 99% favorables.
I've been hanging around here for about 3 years. I found GBO when I had only one Handi, a .45-70. Now I have eleven of them, and I'm thrilled with all of them.
The general consensus here it that the .357 is one of the "must have" Handis along with the .30-30 and .45-70. Many of us have happily reamed them to Maxi and never looked back.
When you get the rifle, pour .38s and mags through it, and I think you're going to

without any problems.
Good luck,
Pete