I am looking for advise on steps I can take to find out if it is possible to include a 5th unit in the backyard. 

Thank you very much for taking your time to advise @Bridgette Delv.Very good point “what I have to lose”Thank you agin and god bless you.

@Fay Brown every single time I’ve bought property there’s been some compromise.It is extremely rare to find exactly what you want in any market, though obviously it’s easier in buyer’s market (ten years ago) then a seller’s market (today).A good real estate agent should be able to help as far as what are realistic expectations and what are some areas where compromise might be advisable, in order to open up the field of possibilities a bit.It’s definitely true though, that type of financing (or lack thereof, in your friend’s case) has no effect on determine what’s out there, available in the market for making an offer.My usual advice here is: Make your own market.

Admittedly, your profile would seem to indicate you are..If you are flipping, I’d definitely advise starting your LLC.

It sounds like you are trying to violate HOA rules (because I suspect this requirement was put in place by the HOA to prevent what you are trying to do).While this might be possible by having a master lease an then adding/removing roommates as needed, it might not be advisable to make an enemy of the HOA and your rule-abiding neighbors - In many communities, the HOA can make your life miserable in many, many ways, and you want to avoid their radar (and their hit list) whenever possible. 

I believe more than a few tax pros on this forum practice what they preach and invest in RE themselves (myself included).Judging by your description of your current situation and the hypotheticals on your horizon, I would advise you to look for continuous guidance as opposed to a single consultation to clear this one hurdle.This is a growth and preservation of wealth plan.

@Edith Alvarado de Cortez i use LLC's for mine, however every situation is unique so it's usually best to consult a lawyer for all this so they can set you up the way you need to be in regards to what kind of entity you need, it could be an LLC, S-Corp, etc... and then they can advise you how to hold them such as LLC's owning LLC's, your trust owning an LLC, etc

Nathan G has given a magnificent answer and you should follow all the advise that he has presented.

WE DO NOT mark-up eviction lawyers (in fact we only go 2x a year for 200+ units and mostly for non-payment - life happens)WE DO NOT put in deadbeats or troubled tenants we will need to evict (we have to deal with them - really, life is too short)WE DO NOT advise our clients to buy in crappy neighborhoods or buy crappy buildings because they are so cheapWE DO NOT put our clients in harm's way legally because we know the legal landlord/tenant laws and what to avoidWE DO NOT take on Landlords that do not see the value we add and want to nickel and dime good quality servicesYou must have had a run in with a REALLY BAD manager to have such a skewed view of the industry.WE DO screen for 3.75% rent/debt ratios, evictions, crimes, felonies, level 3's and ALWAYS cross-check in our networkWE DO screen out landlords too because let's face it, there are some bad ones, and we don't need their business eitherWE DO market the snot out of our rentals on over 30+ apartment sitesWE DO market with pictures, videos, BLOGs, website, referral programs, word of mouth and our landlord referral networkWE DO know title-real estate-eviction lawyers, contractors, REALTORS, and have a wide network of professionals on callWE DO get discounted rates and preference on service because of the volume of work we provide our contractorWE DO have a 100% guarantee on placed tenants, if they default within 12-months, the next tenant placement is free on usWE DO frequently see the property and build relationships with the residents AND neighbors to be boots on the streetWE DO know which landlords are selling before the hit the market and give pocket listings to keep the management contractIf this ain't worth $85 bucks, let's keep going.

Please advise if you have any additional questions.