Recently, our real estate agent did a market analysis and estimates we can sell for between $575K-$585K, resulting in a net gain after all of our fees of about $100K.

A good way to gain money for retirement, etc..

But if you had access to 100% financing for a fix/flip, would you be at "that point"?

It’s better to start small and gain experience than to get stuck overanalyzing.Keep the questions coming!

They can help you navigate code compliance, especially with accessibility and egress requirements, and provide a clear budget before you begin.

My main question is whether it makes more sense to go the seller financing route and pay off the principal in 8–10 years or stick with a standard 30-year loan.My thinking is that the tax deductions from a mortgage wouldn’t outweigh the potential equity I could gain over those 8–10 years.

If your portfolio is large enough, 5% is better.Now, some people believe that this diversification reduces the chances for a large gain.  

However, longer-term bonds (1-5+ years) are subject to interest rate volatility:If rates rise, bond values drop, potentially leading to negative net returns.If rates fall, bonds appreciate, but gains are capped by their fixed coupon rates.While Treasuries provide stability, they offer limited upside and carry hidden risks for medium- to long-term maturities.Why Real Estate Is a Stronger Option in Today’s MarketMultifamily real estate, particularly value-add properties, presents an asymmetric risk-reward profile that Treasuries simply cannot match.

You would then have two loans, one on your home and one on the refi to access the equity on the investment home.Why not just use the refi cash out from your home loan for future deals? 

The great thing about living in a high cost of living area is that your salary / wages are hopefully also very high.If you are a new college grad, I would focus the next 1-3 years on increasing your salary as much as possible(gain new skills, new certifications, change employers, etc).Once you make more money, you can easily get in a position to buy a property on a more frequent basis.Best of luck!