If its cold, your property is poorly insulated, and the tenants crank up the heat that bill is entirely possible. 

Frost the window, insulate and cover it over with your new surround.

Especially with the noise I create from power tools, I would be able to insulate my yard with more foliage to absorb the sound.

Sounds like a lot of work, water damage, and possibly replacing the floors, all the insulation, fixing plumbing, possibly electrical (which if there's a leak could be a shock hazard so be careful) Termites?

Putting money down insulates you from that.

Electric rough in starting this week and then insulation goes in.

In my case we didn't actually raise the roof itself, we just removed the ceiling joists, adding insulation in between the roof joists, and installed drywall.

Would the interior planking help at all with insulation since the house is so old??

The will start air-sealing Monday and I expect insulation will begin on Tuesday.

I had jacked up the insulation to about 24" (90% plus of HEAT GAIN is through the roof), I had SOLAR SCREENS on all south and west facing windows, all of my windows and doors were well caulked to prevent air leaks, all of my units had electronic/automatic set-back thermostats, whenever I replaced a roof I went with a ridge vent to improve air flow through the attic.