As was noted, fit is far more important than hardness to prevent leading. As far as Micro-Groove barrels go, they can shoot cast bullets just fine, but they typically need a larger bullet than a ballard bore will.
Whoever told you the 45 Colt was a good round to learn reloading on gave you good advice. Those old straight walled black powder cartridges are very forgiving. The only thing you need to be careful of is the possibility of double charging. Modern smokeless powder take up much less room than BP so if you're not paying attention you can double charge the round and have a real problem. That's how guns get damaged and people get hurt.
Unique is a good powder, but for a plinker I would recommend Trail Boss.
TB was designed to produce mild loads in old BP cartridges used by target shooters. It's unique design makes it extremely bulky, virtually eliminating the chance for a double charge. I've used it successfully in .38 spcl, .357 mag, .45 Colt, and .45-70. It's good stuff.
Anyway, welcome to the wonderful world of reloading. I find it to be a rewarding and relaxing hobby, hopefully you will too.
GH1