I am new to BRRRR, I have been flipping houses but want to supplement my income with positive monthly cashflow in rentals.

I will supplement by wholesaling and possibly flipping with partners once established in a market and cherry pick the deals for my BRRRR portfolio.To begin virtual wholesaling Find a virtual mentor Hire Virtual AssistantBuild buyers list Pull prospect lists to text Find photo/video provider Text and Funnel leads for qualification Contact qualified leads to better understand their needs Run the numbers Hire photos/vids Negotiate terms Distribute details to buyers list and sell to buyer

Or any supplemental income. 

Will all these expenses be shown on Supplemental income and loss form (Schedule E) or some where else?

Supplement it with online networking like here on BP and other FB groups. 

I hope to secure a few parcels to supplement our retirement income in the next few years.

You can use the Blumberg A-55 'New York Apartment Lease' these are standard forms that you can buy online or any stationary store (probably cheaper since they sell them loose)...I own two NY co-op rental and use it in both...another alternative if you work with an agent is using REBNY form which is very similar and would agent probably suggest with no charge to you.In addition I follow my old landlady (an RE Agent) practice of supplementing it with a rider (copied hers) in which I stress/modify/add term which are important for me (for example that tenant cannot Airbnb the apt).The co-op is a company which have their own interest which not necessarily align with yours...it just happen that sometime they allow you as a shareholder to sublet your unit.   

Are they supplemental to a central system? 

@Louise Fuller you are correct, I do recall he supplemented the rent savings with personal savings.

(And serious law suits don’t happen nearly as often as you might think)When you purchase under your own name, you can take out both a landlord policy on the property (similar to a homeowners policy), and supplement it with a $1-2M umbrella policy that should protect you from most issues.