A - Yes, generally as soon as the rehab is done and you have a signed lease. start my refi process the day I close on the purchase.
B - Local portfolio lenders are your best shot. Get on the phone and start calling local banks. Ask for their commercial lender. I
C - Just like any other loan. W2s, ~3 years of business and personal tax returns, balance sheet and cash flow statement.
D - Not for small residential properties. As least that's been my experience.
E - Max I've found is 80%. 75-80% is typical.
F - For a cash out refi with a local portfolio lender, it will be the new appraised value.
Your example scenario makes me think that you'll be leaving some cash behind locked up in the property, which is not bad in itself if you're ok with that. You have to add in all of your closing expenses twice (purchase and refi); if the rehab budget is between $18-20k, plan on $25-30k. Generally for BRRRR you want purchase + rehab costs to be less than 70% of ARV, unless, again, you're ok leaving some cash locked in the property.