If you have a chunk of money to get going I'd personally buy the biggest thing you can if you don't I think house hacking into a 4 plex is great. 

Those are usually not local hard money lenders.

My walk through estimate was roughly 60k, Hard money was 12%.

You have zero control over the stock market, whereas when you do private lending, you have significantly higher control and contractually guaranteed return on your money.

Going direct instead of having a GC do the work will save you money too since that GC will put a percentage on top of work. 

I feel like having such a low payment and rate make it stupid to choose selling the house, but since I haven't been in this position before, I thought I'd ask here. to d The other consideration you would want to consider is your VA entitlement if you are hoping to buy the next house with a VA loan.

Some properties actually lose money each month but gain value through appreciation.

Is it hard money loans, angel investors, etc?

I would like to put the money into purchasing another investment property.

If you are planning on living there (ie in 1 unit) then you are house-hacking and this is a different calculation consideration then renting out both units and making it a true investment.