We are in our mid 20s, we have a combined student loan dept of $80,000, have $10,000 saved up, and are approved for a $120,000 loan.

There are quite a few properties in the area already selling in that rate and close to the same size and the market is swinging up really quickly.This is the property here.https://www.zillow.com/homedetails/17-Arrowwood-Ci...Also posted it for sale for a wholesale fee if another buyer bites if I don't purchase it.https://www.biggerpockets.com/forums/517/topics/60...The seller will also pay a deposit of 17200 at closing for the option to rebuy in 3 years if they don't they forfeit the deposit.

and someone else is helping us paydown the mortgage for the Santa Clara homeWe ended up buying a home with a huge lot size in Milpitas (12K) and now I am looking to add value to the plot by adding an ADU & expanding rooms & generating some rental income. 

First off, Thank you for your service, My daughter is in the military also, she makes me proud. 

Just go in to any small, community banks in your area that service their own loans and don't sell them on the secondary market. 

What service have you found to be most cost effective?

Im seeing very little in the way of cash flow properties but wanted to seewhat you all though about my inputs.Im making a few assumptions mainly looking at multifamily up to 4 units with 10% down (I know this is low but I've found banks that'll do that in my market for properties under 500k) then I account for maintenance/debt servicing from past experience (wondering if people have a better way that would take into account property age and condition for maintenance estimates), finally I set vacancy at 1 month a year (not sure if that is reasonable either). 

What size cabins rent best for you?

Having umbrella insurance or having an LLC for your property management services is a great business model to protect yourself.

Your books are where all activity is centralized.If you find yourself spending too much time on Quickbooks, it's time to outsource it to a competent bookkeeper (preferably one who specializes in real estate), especially with the size of your portfolio.