I am moving into an apartment closer to work this month, and was thinking about trying our Air BnB to rent my extra bedroom.

Just starting out1-have mortgage, personal loan, and car loan. 2-not much extra money 3- i want to start investing but when do i start?

If you do not include it now you may have difficulty adding it later.  

If they get well each month and aren't bad tenants in any other way, keep collecting the late fees making the extra income. 

I can't pay cash but can pay a down payment and would likely pay extra, especially after the next few years go by.2. 

I tend to work with military communities for rentals and flips, but I am always looking to learn a few more techniques to make some extra coin.

I think you should plan on compensating yourself for it.I hope this works out for you but just wanted to share my observations in hopes of it giving you extra things to think about.

Also to buy only properties where I can add value and/or have built-in equity as a bit of a cushion for if/when the market takes a dip.It’s not that I’m expecting to sell anytime soon, but I’d like to have the option to sell and the extra equity created allows me to do that.Finally keeping plenty of cash reserves and sources of capital open (lines of credit, private money).

It’s still possible to pay down the house early by making extra principal payments.

Grade school math itself isn't difficult. i think the questions come up when you are unsure which numbers plug in to the equations.