Use brass brushes if you can splurge for them with your cleanings. Nylon brushes are more abrasive than brass brushes IMO.
I personally also like that with the brass brushes I can really work them to get the rifling cleaned out without any harm done to barrel. I never use a "heavy" solvent on my guns, I always use milder solvents (Hoppes #9) and oil - or my favorite method for specifically black powder, dish soap and warm/hot water followed by a thorough drying and oiling.
I've never really understood the "break in" procedures that have been around only the last few years. I was taught three steps to a new gun though that I've always followed and never had a problem with using, the other seemed an unnecessary breaking-in of a gun/barrel in a more excessive/aggressive manner:
1. Thoroughly clean and oil your new gun (and magazines) before taking it to the range. Familiarize yourself with the working/moving parts of the gun (trigger, hammer, springs, slides, bolts, pins, catches, etc.) because in step 3 you should also be looking for any unordinary/excessive wear to those parts.
2. Thoroughly go out and have fun with your new toy. Take a break between sessions/magazines because while you will want to shoot ~100-200+ rounds on its first day (a good thing), you don't want to get the barrel "hot" on the first day, just warm it up.
3. Clean it when you get home, take your time studying the results of your outing on it (step two) and noting where additional attention may be needed to cleaning/oiling it in the future.
If you're a first-time buyer, I'd recommend going to a real brick-n-mortar store and dealer, especially if you're concerned with any of this breaking-in stuff. They'll walk you through the FAQs and get you setup with your purchase. Also every gun I've picked up from a dealer seems to of gotten a cleaning/check done by them before they hand it off to you and I would consider range-ready, I never find a spec of crud left in it, while "out-of-the-box" they came in from the factory guns I've found to never be 100% clean oiled and range-ready (IMO).
Fantastic new addition to the collection and hunting buddy ya got there Rog!