A great step to help you narrow focus, budget, etc will be to speak with an STR focused lender.. contact @Joseph Chiofalo he''ll be a very patient mortgage guide. 

Hello :)There is definitely more out there, i was once in your shoes and now completely got out of corporate world.I am a lender and investor from Houston, TX.

This means all expenses, including the mortgage payment, is being paid by the tenant. 

Most lenders dont do construction loans ...most  construction lenders - wont do loans for  rental  properties 

And then use the $2400 from my first rental towards my 2nd house mortgage?

Look for hard Money for %80 of each property, then do a cash out refinance and pay the hard Money Lenders.

During the term period, do i take over mortgage payments and pay the seller a rental fee/rental premium from the cash flow?

Context: I’ve been using MLS, realtors and wholesalers to seek out my first investment property (debt free outside existing mortgage, $100k cash saved, stable income), since my network is fairly new and limited as a green investor.

a plan to refinance our current mortgage as well as get a HELOC.

@Huiping S. if you have a mortgage then the SDIRA will have ubit and a 990t will need to be filed.