I'm looking at investing in a short term rental in Jacksonville, my budget is fairly modest though, up to $300k so I'm not looking to do a high-end STR.

Yeah you’re fairly safe as a landlord.  

I also know Arizona is fairly investor 'friendly' and has fairly low property taxes.Interested in purchasing small multifamily properties (2-8 units) depending on the property and numbers of course.

So just don't open yourself up to fair housing violations if you do deny them.

I'm about ready to retire so I'm not looking to compete in a bidding war, mainly looking for a fair deal that I can rehab or a turnkey with some cash flow. 

Taxes are calculated on the gain (e.g. sale price - purchase price + expenses, broken down fairly clearly by @Jake Baker) not just on the sale price.The tax treatment on sale of a Primary Residence vs.

If they don't you personal financial situation plays a bigger part in securing a loan. 

Most of our investments we look at IRR (time value of money) to determine which investment is a good fit for us at this time - which factors in returns, risk and time of investment - is it a short term investment we want to get appreciation play or long term fixed income investment.

He was helping a friend in a weird situation but $700 was fairly close to what others rented for.

Not as good as a separate metering, but its less cost and seems fair to me with little added effort for billing.