Your mortgage has nothing to do with your taxes.Here is a very rough starting point, however the actual calculation will involve more details:1.

Per this NY Times article, the average American knows around 600 people.https://www.nytimes.com/2013/02/19/science/the-average-american-knows-how-many-people.html#:~:text=The%20average%20American%20knows%20about,do%20you%20know%20named%20Kevin%3FPer the US Census Bureau, the average American moves 11.7 time in their life, which based upon an approximate lifespan of 84 years, works out to be about every 7 years.https://www.census.gov/topics/population/migration/guidance/calculating-migration-expectancy.html#:~:text=Using%202007%20ACS%20data%2C%20it,one%20move%20per%20single%20yearSo, if the average American knows 600 people and they each move about every 7 years, that means that the average American knows around 85 people that move in any given year.How many of those moves do you want to be involved in?

Be very careful who you take advice from online, you should get involved with a local attorney and a local realtor.

Without my wife's direct involvement, I think some of our homes would have struggled to stay afloat.   

And this does not even involve business or real estate!

I've selected Collin, Denton, and Grayson counties as my investment focus.My goals involve investing in small multifamily properties and long-term rentals.

Are there going to be banks involved, creative seller financing or all cash? 

There is no seasoning requirement involved since the property isn't a short sale and it isn't someone buying REO from a bank with a seasoning requirement.

Plus new folks do a very poor job of screening the buyer for Ability To Repay (ATR) which involves pulling full doc and calculating the borrowers DTI, honest income, honest debt payments, prior debt payment histor (FICO) etc etc.Plus shockingly (or shocking to sellers) if you bought this investment house, fixed it, then are selling with financing you are selling "inventory" and y9ou owe taxes on the gain in the year of sale, you are NOT able to use installment sale to spread out paying taxes. 

@Geoff Engel If you don't want to be a landlord but still want to be involved with investing you could be a private money lender for flips or in partnerships and bring the money to the deal.