You are interested in real estate investing and are looking for resources to develop your knowledge.I work with a lot of doctors and busy, high income earners to help them build real estate portfolios to slow down at work and offset some of their W-2 or business income.Some books to consider are Multi-Family Millions by David Lindahl, Investing in Real Estate with No and Low Money Down by Brandon Turner, and Equity Happens by Robert Helms & Russell Gray.Some You tube channels to follow include Get Rich Education, Ken McElroy, Jason Hartman, and the Real Estate Guys Radio Show.Yes, until you are making attending physician money, I would house hack the house you live in by renting rooms or buying a duplex as a primary residence with low money down.To Your Success!

I use MyFax - I've used them for years with good success and no problems.

Even If there is no requirement for a medicine cabinet I might move it to the side on the left side, And have a mirror cut to fill the entire back wall up to the 7 foot mark if possible for tall people.

If you refinanced the same 400k with no PPP at 5% that would be a payment of 2147, or a savings of 514 a month.

Just doubled your earnings and have no debt.

No update of common area finishes although clean and well maintained.

We also have a "no pet" policy were a couple tenants brought in pets that caused issues. 

You should be able to but if you want to make sure call a title company in your area and ask

There is absolutely no way we are fitting more than 6-7 guests in the property, so I'm guessing your home would be about the same.

In terms of your grandfather living there as long as he's not the owner having a dwelling fire/rental property insurance policy is appropriate.As @Greg Scott pointed out he should have a renters insurance policy whether or not he's actually paying rent.In terms of liability coverage, that depends on what you have to protect so there's no one-size fits all approach.