I have never built anything, only purchased already built properties and I need some advice.Thanks!

Where are you looking to purchase in?

The real estate investing industry uses "Classes" to rank property performance risk, but there's NO agreed upon industry model:(Here's what we use for our Metro Detroit market:Recommend you first figure out the property Class you want to invest in, THEN figure out the corresponding location to invest in.Property Class will typically dictate the Class of tenant you get, which greatly IMPACTS rental income stability and property maintenance/damage by tenants.If you apply Class A assumptions to a Class B or C purchase, your expectations won’t be met and it may be a financial disaster.If you buy/renovate a property in Class D area to Class A standards, what quality of tenant will you get?

Both properties have a substantial amount of equity that’s essentially sitting idle.Would it be a good idea to tap into this equity (through a HELOC, cash-out refinance, etc.) to fund future fix-and-flip projects or purchase additional rental properties?

Purchase Price:Focus on areas where the rental rates align well with your purchase price.

Quote from @Eli Kim: So I  currently have 3 properties and I want to purchase another one but the issue is I’ve maxed out DTI.

You should be able to do a pretty decent update with $50k (purchase price not included).

For path #2, you mean purchase & renovate a 3-5 unit building right?

In the Bigger Pockets free book, "Real Estate Rewind", as one of the 11 co-authors I wrote about one such Tax Sale purchase and made money but not enough money to warrant the risk involved.

For the BRRRR process I plan on using a hard money lender for the rehab process for the SFH's but what I'm not sure of is, should I purchase a duplex and rent one unit out and live in the other or should I just rent for now, not purchase a duplex and just purchase a SFH with cash and start BRRRR'n immediately?