I prefer to go the HELOC route because you can use it like a checkbook and only use it when you need it. 

I prefer being 5-10% below market.

At least that's the setup I prefer, others may do something different.

@James Sebastian your response is pretty well thought out already, my only recommendation is to include a personal invitation for them to contact you directly by phone, email, U.S.mail, or thru your attorney if they prefer. 

What is preferred?

That is just our business preference.

Preferably one that actively purchases investments like you are purchasing.2) An investment specialized local realtorThese 2 specialists will give you a list of practical solutions, and then you can create a road map and the 3 of you can work in lockstep, with the same goals to get you there.

I'd prefer this loan because it doesn't require any upfront costs, however I can't find any information on refinancing into one from an FHA loan. 

Is my problem specific to my lender that isn't willing to work on multiple deals at a time from different sellers or am I hamstringing myself by thinking that I should stick to using one preferred lender at a time? 

As you experience, grow, and learn more, you'll have a better understanding of how things work and what ventures may be best suited for your personality and lifestyle preferences.