The re-lining procedure only makes sense in very select cases where the pipe structure is still sound, but the surface is very far gone, or the pipe is under massive tree roots.  

The team you work with is equally as important as selecting the market, it sounds like you understand that.

@Jeff White made an excellent point. 

A seller I dealt with before has offered me his last property as he plans to retire at an excellent price.

I feel it's better to move them out, clean the unit up, and rent it at market rate to someone you've selected.

If so, can they handle an increase or should you terminate their lease and start fresh with tenants you've selected?

I have no real niche selected although I've been researching for a little while now and am leaning towards purchasing a duplex near the base or value-add while living in a single family, perhaps to rent to other servicemembers after my tenure there.

You're going to want someone very familiar with the area to guide you in your property selection.

We pulled the county data and sifted it via excel. 

Pick a good building in a good neighborhood, then spend time with your prospective tenants to select the best.Good luck!