new Investor using first time home buyer on 4plex

Hi I am 21 and I have been doing my research on buying my first home. I starting learning about multi unit complex's and found out the you can use your first time home buyers to purchase a 4-plex. however you need 10% down plus closing costs also you need vacancy to move in and claim it as my primary residence for 12 months and depending on how many unit are empty I will  have to cover those costs until I can find tenants.

4-plex's around my area got around 400,000.00 so 10% is 40000.00 as I said I'm 21 and just starting to build my wealth and net worth I am putting 300 away every month and have a small construction company that I use to do small jobs for people. I am using that to super charge my savings I have calculated the I can save about 20000.00 by January 2019. that is less then halve of what I need I'm am considering a private investor but have no idea where to start. 

I have a goal of having 30 units by time I'm 30 and wondering if there is a way I can get to that maybe another way where I don't use a private investor I would like to do this without having that liability since there is a lot of risk associated with that already. anyway let me know what you think.

Thanks!!