Recently several of my investor clients have leveraged equity in their primary or investment properties as down payments for purchase acquisitions by obtaining a HELOC or fixed rate second mortgage. 

If you are making larger orders you can make those through their pro-desk or through their pro-site and get discounted pricing and probably average 15% off!

Definitely check in with @Joseph Chiofalo for Jumbo second home and investor loan products, we just had an unbeatable rate and appraisal waiver here on the coast. 

Also not sure when you bought your primary residence, but most likely rates have risen which means your payment would go up. 

or any recommendations on which is the best Bank/lender to get one with the best rates? 

You would never ask an attorney to lower his rate for doing his job and telling you what to expect. 

Look on Vrbo and Airbnb and see if bigger houses are booked at good rates.

"McAllen was recognized as the third safest city by SmartAssest.com, which analyzed a core set of common safety factors, including the following five metrics: violent crime, property crime, vehicular mortality rate, drug poisoning mortality rate and the percentage of the population engaging in excessive drinking."

So in my case, we selected June 1st - June 29th, adjusted the minimum stay to 2 nights for that period, and upped the rent for that period to STR rates. 

As for your plan to snag 4 in one year, that just comes down to your finances at that point and the interest rate.