I have the reserves in place for the 5% down payment, 15K for emergencies, and have no debts! 

Figure out what each of you want and what reservations you both have and work through it.  

You still need the reserves for now, but you are in a good spot.Your real choice next is where to invest.

In both scenarios, I will use the equity in my first rental via HELOC to either cover the conventional loan's down payment and fund the rehab or to fund the hard money down payment and meet the reserve capital requirements.

Should i refi my units which will kill my current cashflow and impact my reserves?

The guests paying for the reservation are likely a couple who want a king bed. 

And then there are others that are just pump and dump due diligence schemes.. now when i googled this company their web page came up .. but there is also complaints and a rip off report link.. so i would read all that stuff first.. take it with a grain of salt.then look deep within and ask yourself if with your business acumen and 2 to 3 years of tax returns.. and your fico and your cash reserves can you do a 1 plus deal.

If you had the capital for the down payments, reserves, closing costs, etc., would you advise buying 4 SFHs or 2 duplexes.

Commercial requires the property to be livable (not subject to), usually a 95% to 100% occupancy ratio, DSCR (rents) at 1.25% or higher, PFS, Strong assets, 12-18 months reserves, Fico above 700, I have seen lower but rate will be higher and in most cases cause the DSCR ratio to be under 1.25%.If you own a primary you might be able to use an SBA type program but those are not great.

Make sure you read the bylaws and understand the current reserves and upcoming large expenses.Good luck