So, you can activate a channel remotely from your phone, tablet computer, etc (Yes, this would involve a guest sending you a msg, if it’s a channel that doesn’t do #3)3.

That said, VRBO doesn't do auto messaging and that's a PIA that makes a channel manager a nice tool to have, but often the cost isn't worth it until you get at least 1 more unit - again, my opinion.  

One of the biggest risks I observe with flips and first time investors are instances where the project goes over budget or gets stuck in mud, can't sell and even worse the borrower doesn't have the credit profile to refinance out to a lower interest lending source if borrower is required to hold the property as a rental. 

You need to know for sure.Even if you raise the rents, the property is still a negative cash flow, so it doesn't make sense.There are always comps.

Tell her if she doesn't agree to the new rate, she give notice to vacate and provide move out instructions. 

I'd sell if I were you. 1) I don't like HOAs and certainly not for STR or MTR 2) the numbers don't make sense for you to invest in a big kitchen/bath renovation 3) it doesn't look like it's appreciating very well.

See this BP blog for a numbers comparison - More Units Doesn’t Mean More Money—Why a Single-Family Home Can Beat a Fourplex.Stay focused on your goal, financial freedom; not following popular dogma.

You should talk with lenders to get an idea of what you can actually afford though it doesn't really matter if you talk with an agent first since most agents will have lender recommendations.

The reality is the opposite - if it's not in writing then the PMC doesn't have to provide the service or can charge extra for it!

Prices are high, and rental income usually doesn’t make the math work.