I am interested in investing in Tax Deeds, but I'm skeptical of the technicalities of it that I'm uneducated about.

With HOA and other expenses like insurance, taxes, it will generate around negative cash flow of around 700 dollars per month.

So, if something goes wrong, now you've got a loan on your house that you may not be able to immediately payoff.As mentioned, don't forget about your taxes. 

You're new mortgage, taxes, insurance, and hoa will equal $800, so you'll have a positive $200 cash flow each month.

Realty Transfer Tax. 

If they charge more its considered an illegal tax.

Does time taking care of (mowing/landscaping) and managing (keeping records, paying HOA dues, paying taxes) my vacant parcels count towards my 750 hours of being a real estate professional?

If there is something special in your scenario that is causing the issue you always have non-QM products to fall back on like DSCR (qualify based on the asset, only works for investment properties) or Bank Statement loans (qualify based on income, no taxes required, great for self employed).

Do remember when thinking to MTR to calculate in 7 days and less avg stays to qualify for material participation when self-managing STR for your tax year deductions as a business against your W2 wages.

I know there are certain liability protections, but I'm more interested in the tax implications.