Post-Purchase Advice: Debt Counseling and Buying Again

[Colin Friend]

Hello, I am 28 years old, single, and just bought my first home.  My goal is to own my first multi-family by 2019.   At that point I will rent out my current home, live in the multifamily and rent it out.  I need advice on building a plan to make this a reality.  My financial situation is as follows:

70k/year income

Renting rooms for 1k/month

10k Savings

12k 401K

10k 401K Debt over 5 years (100/paycheck)

~300k mortgage over 30 years (1500/month plus 200 PMI)

6k student loan (100/month)

Living expenses (discretionary and repeating) 1k/month

Extra yearly income: 20k

My real question is what to do with that 20k. How would you handle the debt while also positioning to buy a multi-family in less than 3 years? Pay 20% into the mortgage ASAP to drop the PMI and then refinance? Split payments into mortgage and 401K loan so I could take another 401K loan? My employment situation is stable and I stand to receive a few raises over the next 3 years as well.

This is my first post, and I am hoping those of you with more experience and financial savvy can share some wisdom.  Thanks!