You always have the potential to refinance down the road if you have the option to get a lower rate. 

My current lender says I cannot refinance my loan until 6 payments are made.

Yes, you could refinance out and capture your VA eligibility, but the debt you have secured is low, and you can hold the properties for up to 15 yours without doing a 1031 exchange.

I am offered a 80% LTV cash out refinance (I put down 25% on the 4plex).

I'm assuming you find a bank to refinance the loan but is there any risk of the banks rejecting this loan?

Suggest a 3-5 year balloon with no prepayment penalty so you can get the property complete and rented and then refinance them out.

I am looking to refinance my single family home in Mariposa California.

@Cody Stevenson It may be worth looking at what a refinance would do for your numbers on your Denver house.

I don't see any reason that your lender on the re-finance would require a down payment, usually your built in equity should be enough for them.

X for kitchen, Y for a bath and add ons like roof, A/C etc which are easier to close in on as far as value.That being said, you could refine "Kitchen" with  small Kitchen rehab 10K, mid size 15k etc  (making numbers up).