Personal Deal Advice - Old Mixed-use Building Acquisition

Monkeys!

Some friends and I are looking at acquiring an old mixed-use building out in a decent part of town. The building is 100% leased with the bottom floor containing one retail storefront and above it are 4 small multifamily units. The building is quite old, built in 1913. 

My friends and I all work full time in commercial real estate, but we are quite junior and haven't experienced many transactions. We are approaching this investment outside of our full-time jobs. We have a business plan and capital ready to go, we are just unsure of a few things. 

Since this building is over 100 years old, I am seeking advice regarding what to look for / ask for when going through the DD/closing process. We are not very familiar with the construction/engineering side of things, so I wanted to see if there are specific things we should be looking out for. I am sure there are also codes or special regulations that come with buildings of this age? FYI, this building is located in the Seattle area and has endured the typical Seattle weather.  

General advice is appreciated too, this is our first time doing something like this. If someone would be open to a discussion via PMs as well, that would be amazing. 

Thank you all!