I don't even have a payment system or anything in place.

Is it a bad idea to use a HELOC to pay the down payment for my first short term rental investment?

Me and my fiancé are wanting to try and purchase new construction homes in class A to B neighborhoods (275-350K) and put 20-25% downs and live in them for 1-2 years while we save another down payment and then eventually move on and make it a rental.We are not looking to scale rapidly.

Rents go up, refinances bring payments down, etc. 

The greatest obstacle in the way of the desire to expand portfolios is the need for cash to use as down payments. 

However, his mom's offer to co-sign shows commitment to ensuring rent payments.

If I were able to acquire my next investment through cash and/or bridge loan, install my section 8 tenant and show a couple of months of rental payments, is there a lender out there that would use that lease and its accompanying Housing Assistance Payment contract I would have with the local housing authority? 

Maybe they can make payments.

My name is Lalo and I'm new here. i live in Astoria NY and  I'm looking to buy my first multifamily property with a FHA loan or something that requires a small amount for the down payment.

Most hard money work as follows:•Rates: 9% to 13% (Most Deals are 11-12%)Terms: up to 36 Months (Most Deals are 6-12 months)Fees: 2-4 points(%) of loan amount paid at closing (Most Deals are 3 points(%))Minimum Loan Amount: $50,000 (For loans less than $250,000 $2,500 minimum fee)Max Loan: 65%-70% of After Repair Value(ARV) 100% Rehab Financing Available (Require 20% of purchase price down payment or cross-collateral)Closing Timeframe: 48 Hours - 3 Weeks (Most Deals are 2 Weeks)NO PRIMARY RESIDENCES, NON-OWNER OCCUPIED ONLY, BUSINESS AND COMMERCIAL USE ONLY.