I'll answer your questions pretending it is 2015:
1.) Private money or family money is best to get started. It is easier to get than anything else. Then refi into conventional or commercial loans, probably need a mix of lenders. Commercial portfolio loans will be quicker.
2.) You just buy as many as you can and then figure it out, there is no way to prepare, you just deal with it. You'd be surprised what you can do, if you have no choice.
3.) Local banks. Spend some time talking to investors, asking for names, talk to a lot of banks. Every bank is looking for something different and it changes over time.
However, we are not in a BRRRR market anymore, you'd be sailing upwind.
After more than a decade I have stopped BRRRR-ing a couple of years ago when the market started going nuts. So we are not buying as much anymore, but still growing. I closed two properties last night actually, both move-in ready, fully updated and rented. I was able to negotiate about 10% discount that was purely circumstantial, I'll let time do the appreciating passively instead of running a 6 months construction project with holding cost.