2 family heating updates and uninsulated exposed basement

[Luca Mastrangelo]

Hi everyone. Not sure if this is the best forum to post in but ill start here. 

my property is a very old , circa 1900, 2 family in south eatern ct. The foundation is typical field stone basement. It's a concrete slab for most of the basement but there is an appeox 300 sq ft addition where a 1f bedroom is that is built over a crawlspace but also with field stones for the foundation walls .  The bulkhead is wood (odd size) and not air tight. The steps going down are 3 large blocks and the door at the bottom is prob original, wood and has a lot of gaps around it. The bulkhead offers more defense against critters and the elements.  The sill plate is rotted in places. During heavy rains I get water in the basement through one corner primarily. It pools in one area. I have (2) 50 gallon electric hybrid hot water heaters down there. Not much else.

both of the units use electric heat and the heating bills are alot in the winter months. Each room has its own thermostat.  Every tenant has had this issue,more so the first floor unit because they don't get the benefit of rising heat and is larger. I lived in the 2f unit for 5 years and can attest to this. 

im considering putting in a mini split with heat and AC (prob 2 cassettes per unit) to primarily supplement heat in the winter. I know they're electric too but should be more efficient and better at heating the space. 

im thinking I need to address the basement first though since it's completely uninsulated and pretty exposed but before I can do that would need to address the water issue,sill plate and probable repointing and some kind of paint treatment. I wish I could just live the house and put an entire new foundation down but that's not going to happen.  I looked at some DEEP energy conversions and their basement refreshes look ideal but not sure what the cost of that is. 

i did do an energy assessment a while back and in 2014ish blew in over 2' of insulation into the attic space, so that is good there. 

thoughts on where I should start this effort? Other heating systems I should consider? Anyone have experience updating old fieldstone foundation and rotted sill plates?

TIA

i