Paying down a mortgage quicker gives advantages if you believe the appreciation outlook is high because the debt pay down will give you more benefits when the property appreciates.

In light of current high rate environment, if you were an investor/developer, and you were about to start a 30 unit residential/commercial mixed use property (ground level a few shops, rental apartments upstairs), what percent of rate return are you expecting for your initial capital? 

Ideally I would like to purchase a apartment condo (1000 sq foot) in the Mountain View Sunnyvale area and pay additional money instead of paying rent and building zero asset.

That's the amount the property has been appraised at with two homes, waterfront, and a large metal building with a one-bedroom apartment.

HiI purchased a 14 unit apartment complex 3 years ago.  

Potentially, but highly unlikely.

The big brokerages do offer great support, but your fees will be high.

It's an 1890's Queen Anne that was chopped up into an upper apartment with existing long-term tenant, and a hair salon downstairs that I converted into a 3/1 Airbnb.

I have been looking at apartment complexes.

@Joseph Turner, if you're looking to buy in CA areas with high levels of appreciation, I've had clients take out a HELOC or 2nd mortgage and pay back the HELOC or 2nd with a cash out refinance once values appreciate.