We are working towards full time investing but the W2 income is setting the foundation for us.

In general - Unless you know the property has only skin-deep stuff you can fix FOR SURE - I'd hire an inspector to look for stuff like foundation issues, moisture invasion, everything is to code, major mechanical stuff, life on expensive stuff like HVAC/roofs.MHs a little easier though, but don't know the level of rehab you want to do.

Crime rates, sewer inspections, electrical inspections, plumbing inspections, foundation inspections.  3. 

Roofs, kitchens, bathrooms, foundations, plumbing, electrical, windows, HVAC, hardscape are all expensive. 

Research published today by the First Street Foundation (a research and technology nonprofit) shows that FEMA flood maps underestimate the risk to homes/businesses by 67%.

Build your foundation of knowledge and then get started.

The first agent pressured my wife and I to offer on higher-priced homes, so that toward the end we narrowed our criteria to only nonnegotiable items: The house had to have a good foundation, sell for under $100,000 and be in the school district we needed.We purchased our starter home, much to the first agent's chagrin, and after the deal, we agreed not to work with her again.For my second home, I worked with a referral agent.

I don’t know if a slab foundation is allowed in Somerville just cause every house has a basement...

The property is good structurally (sturdy foundation, good roof, but I will get it inspected), but the inside needs a lot of work.

I would strongly recommend reading "Rich Dad Poor Dad" this is a great easy to read book that will lay down a great foundation for your financial future.