I am selling one electrically heated unit this summer, and in another I have increased the insulation and put programmable baseboard thermostats in an effort to mitigate bills for tenants.

Removing all interior plasterboard, ceiling, insulation and kitchen/bath fixtures. 

The salesman at Coburn's told me my water heater went out just in time because in about 1-2 weeks now new federal regulations go in effect that require manufacturers to add a minimum of 1" insulation built into the shell of all water heaters. 

If not (or after you get the leak fixed), replace ALL of the areas where there is any sign of any mold (this means wood, drywall, insulation, everything that possibly has any mold on it) and go test after the next few rains to verify that there is no active leak.Here's is a long list of meters at Amazon.http://www.amazon.com/s/ref=nb_sb_noss_1?

Just noticed some "spots of daylight" through the siding from the inside (I can see the outside through the siding walls in spots - kind of like knotholes)aside from putting up vinyl or hardee siding, is there any way to seal this home before I insulate and finish the inside?

The one additional is improving energy efficiency through better insulation, more efficient windows and sealing windows and doors.  

Replacing like for like is a REPAIR, upgrading is a capital improvement.eg: replacing a single pane window with another single pane is a repair, but going to a dual or triple pane window is an improvement (extra insulation improving both cooling and heating)

The insulation & drywall stink.

Some builders cut costs by installing code minimum insulation and cheap a/c units. 

So during each unit rehab I have upgraded 90% of the wiring as I discovered there were many overloaded circuits that had heat damage to the insulation at some of the outlets & especially the light fixtures.