Has been working well from 2008 onwards till date, but you should have capital and should have alternate income to support the property expenses.

I’m a W-2 employee in a high income tax state.

If you held them less than 1 year you would pay at your income tax bracket but if you held them over a year you would pay LTCG (Long-term capital gains) which for most people is 15%.You'll always be able to add money back into a brokerage account regardless of whether it's the LLCs or your own.Hope this helps

If you get a signed lease for your rental home, your lender will be able to use that rental income as qualifying income for your loan to get your househack. 

Buying existing LTR or STR with proven income that may just need an update or a value add (add more units, add more bathrooms, beds rooms, etc.) and your next one you can try a riskier property that has less proven income.

Is this rental income just added on as income during filing in addition to my income from my main job?

That GRI does include income for cleaning, taxes etc. though normally, which is really pass through expenses for the most part.

As long as all of your expenses are about $500+ less than the rental income I'd say it definitely makes sense to keep as a rental. 

My recommendation if you decide to invest out of state is to choose cities in safe and economically diversified areas with above-average income and population growth.

You can/should sell if you don’t want the steady rental income and you don’t plan on investing in real estate for the rest of your life.