I'm working on a project and the feedback would delightful.

A specific niche to apartment investing is "value add" where you could be in the mix of apartment investing well before 10 years - Jake and Gino's Wheelbarrow Profits is a great book to learn about the concepts of this process. 

I'm in my mid 30s with a wife and five kids aged 8-13 (don't bother with the math, some stepkids some biological in the mix, love them all...haha).

Could go residential or mixed use?

I decided to look over some reviews and they are pretty mixed.

There is a mix of single family, multi family, potential flips, and properties that are already rented.

Every time you send your in-house handyman out for a job on the managed properties, he buys just a few more common building materials than he need for a repair job: an extra bag of ready-mix concrete, an extra box of drywall screws, an extra sheet of drywall, four or five extra pieces of dimensional lumber, extra gallon of paint.

Simple, have separate accounts and don't mix them.

I would like to book the property at much higher short-term seasonal rent rates between May 1 and September 30th.Has anyone had any experience with a mix of seasonal and off season rental for the same property in Massachusetts? 

We converted an old doctors office into a mixed use building with one commercial office space and 3 residential rental units.