Yes, you can do DIY, but it does come at a higher risk of IRS challenge as @Michael Plaks mentions. 

I am lookin for higher rent.

A scenario where you intented to hold but something came up like an unsolicited offer, higher expenses forcing a sale, change in demographics etc.   

Doing a 75% 1st mortgage and 15% heloc or heloan would likely give you better cost of funds all around.If this is an investment property, you can do 80% cash out refi using NonQM loans such as DSCR loans, but at a higher cost/rate than if you stick with 75% loan to value. 

If you are in a state where eviction cost is high and it is tenant friendly you may need a higher credit score to offset default risk and eviction cost.If you are in a landlord friendly state where it is easier to get non paying tenants out you may be able to handle more none payment risk.  

My thought was the higher the better to maximize cash flow.

For larger buildings with financing, it's worth the administrative burden and the potential for higher churn, just for the sake of preserving occupancy. 

A 1/1 with a 4/2 on top is perfect for the hacker to live in the 1/1 and cash flow on the higher rents.2.

Only thing I would add here is to take a birds eye view of the area and try to decide if it will gentrify in your favor so the property appreciates at a higher rate than other areas.

A DSCR loan only removes the income piece and adds a slightly higher rate and prepayment penalty.