Positioned near land we own on West Concord Street, which is slated for a major development of 12 patio homes and two duplexes, this property is central to a broader strategy of enhancing value and transforming the area.

Can anyone give me one advice or one mistake to avoid as  I look towards getting started?

The general reason (avoiding any personal thoughts on wholesaling as a business) is that when you have a license, any fee you get for transacting or assisting in real estate must go through your brokerage and they must take their percentage.

and some areas to avoid ?

I want to use her equity as a gift for the down payment to avoid capital gain taxes.

Given your experience and strong financials, you have some solid options:Commercial or Portfolio Loan: These are tailored for investors and can help you avoid personal guarantees, especially since you have an LLC.BRRRR Loan (Buy, Rehab, Rent, Refinance, Repeat): Some lenders offer BRRRR-specific loans with funding for purchase and rehab, allowing you to refinance based on the new ARV once stabilized.HELOC or Cash-Out Refi on Current Rentals: Tap into the equity on your single-family rentals to secure funding for the 4-plex purchase and rehab without high origination fees.Each has pros depending on your cash flow goals and timeline.

Joseph,Bigger Pockets is the best site on the internet to build a newtork and get all the hlep you need to avoid mistakes and save money! 

This helps to avoid conflict.

My initial question is… Is it good or bad to have individual septic for each mobile vs one big central unit??

My initial thought is to advise them to continue to offer the fee to avoid alienating buyer agents, especially if this is how buyer brokers are creating their short lists to share with clients.