How much more do I need to save, and what's the best (cheapest,fastest) way to find an under market value two-family in a good neighborhood in MA? 

This is really the best place to grow your knowledge in Real Estate.

We just recently closed on two multi-family properties and have been networking locally as much as we can to keep growing our portfolio.

My hopes are to grow a portfolio for my family. 

This would work well for us as our family is growing and we are in need of more space.

This is the best place to grow your knowledge in Real Estate.

I'm thinking to grow (may be I didn't get that point across) which one would you pay off first, to buy another property?

As this is a new home in a nice area I think that it has GREAT potential for the upcoming years, both for growing equity and cashflow, but I don't think that is the right way of thinking as it is being a speculator. 

I'm 21 years young and looking to learn and grow each day with like minded people who've decided this same thing long before myself.

If you do this, I almost guarantee your business will grow quite a bit.