A 4-plex would be ideal and you could play around with doing 1 long-term, 1 mid-term, and 1 short-term, plus you, if it works on your area to upgrade your income.

Do my 3 associates need to create a LLC to be able to do these renovations or can any individual do them, as long as proper permits are pulled? 

These services help identify any red flags that an individual review might miss.Regularly Update Rental Criteria: As fraud tactics evolve, so too should your rental criteria and screening processes.

Ideally, I would prefer to capture their existing bookings after closing, by directing existing bookings to my new listing, but there are some dependencies/uncertainties I'm working through and would appreciate any advice or shared experiences here. 

The seller isn’t an individual, it’s a company that engages in all sorts of real estate activities.

., are all ideal in my opinion. 

Ideally they did not pay over retail because if they did they could easily lose the money they put into the property if the loan gets called.  

Others are owned by private individuals and are for profit ventures, often affiliated with their other business ventures. 

There will likely be a partnership return required where you flipped a house with a partner and lost $120,000.If you sold the other property within the same partnership, it will also be reported on that partnership return.The net result to you is that you will receive a K-1 showing your income / loss which you then use to report on your individual return.If you made no money within the same year, you likely pay no additional taxes / get no additional refund.Best of luck.

Ideally a HELOC is used for less then a  year project where you can refi or sell to pay back the HELOC. 5 years is a long time, things can happen and if you reduce the cashflow on both properties you'll be increasing the risk and having thinner margins.