Should I Sell My Primary House That Is Full of Equity?

[Ryan M.]

About me:

I own two properties
Live-in GF - Owns one property

Primary: ~500k in equity - Condo (Medford, MA - right outside of Boston)

Investment: Paid off ~250k equity.

When I mentioned this to my real estate mentor (who is also a family member, owns 300+ doors in Cali) he chewed me out in a friendly way.  Said I am INSANE to live there, "SELL SELL SELL YOU, IDIOT! YOU MADE A KILLER DEAL, NOW REAP THE REWARDS!!"

His idea is to sell the place as fast as I can, take the 500k and rent a house and use the cash to buy multifamilies in the area.  Or if the housing market is cooling off, sit in your rental with you 500k and wait until the prices drop.

The market in the area has leveled off - Zillow is showing a -1.5% return for the next 12 months, and my trustworthy realtor agrees - things are cooling off and we have reached the peak of this upswing.  

My options are to scramble and list the condo after Labor Day, (realtor estimated that depending on the asking price it will be under contract within 7-30 days) or wait until Spring and sell then.  He does think the market will be strong come spring, but might now be as strong.

I want to get into real estate multi-family investing. I have a decent amount of cash, but far more in equity. I agree that selling is the right thing to do - while I do love my condo, you can't be emotional, so I am okay with selling.

What have others done in the community?  Should I sell now and scamble, or wait until spring? I'd love to hear your stories/advice/experiences.