I've been debt free since my late 20's, have some money invested in IRAs, mutual funds, and stocks, but only passively considered real estate as something that would only come about after purchasing a house to live in.

I have roughly about $15k of credit card debt.

I've read in many places in the BP forums and elsewhere that I should now aggressively attack the debt I carry with prepayments (debt snowball is commonly recommended).The idea of owning my properties free and clear appeals to me (I don't like making mortgage payments, especially the interest portion thereof). 

For our primary mortgage, we are 2 years into a $600K 30 year 3.75% fixed conventional loan.Here are some pros and cons I can think of for each option:Invest as CashPros:Very liquidLess riskyNo interest on cash amount for next investmentKeep higher primary home interest expenses for tax write offCons:Sits in savings account earning 1% until reinvestedPay Down Primary Mortgage and Take Out HELOCPros:Saves $275,000 interest and reduces payoff during to 15 year on primary mortgageCons:Puts primary home at risk if future rental property investment goes badHigher and variable interest rate on HELOCBanks could close HELOC at any time removing my access to the funds for investmentMiss out on tax benefits of higher primary home interestUltimately, our goal is to have no personal debt including primary mortgage, while building a steady stream of cash flow through rental properties over time. 

I work a W-2 job and still have a $13K of student loan, but no other major debt (own my car and small credit card debt) and I have a high credit score.I have been learning and researching on how to analyze BRRRR strategies in my area (Essex County, Haverhill, Massachusetts) but I am stuck on what can I do right now with not enough savings built up get and its only been 5 months with my FHA loan.. should I wait it out for the 1 year mark?

I also don’t like carrying debt so I want to pay cash for my personal residence.

I would also recommend a positive cash flow on day 1 of your ownership and do all expenses except the debt should be around 40% of the gross income. 

The reason is my family business cash flows $700K+ net income/year and only has about 300k worth of debt overall (including a 13 unit apartment complex that is about 50% paid off) so I don't see any problem with getting financing for deals in the 100K-300K range.

If I use ARM for my first mortgage, at the time I buy the second property, how will my Debt To Income ratio be computed?

get rid of your biggest debt 1st then make profits you know?