@Rafael Zavala, you're bringing out my inner building-science nerd...
Mini-splits are definitely a viable option (they can still heat when the outside temps are -15 F), but there are a few things to consider. You really need to get the building buttoned up. The main issue is air sealing. If you're already replacing the windows, put in casements. They are far more efficient than double hung. Seal up all the little cracks throughout the building. Check out AeroBarrier. Amazing new technology. Keep in mind that making a house this tight means you'll probably need to mechanically introduce fresh air, via an ERV/HRV. This is or isn't a big deal depending on the layout of the home. Beyond that, obviously insulate as much as possible, but air sealing is more important.
Keeping the current HW radiators is probably the cheapest option. I think 1700 sqft is too big for a combi boiler. I'm not familiar with the most recent models though. If you stay with something gas fired, go high-efficiency condensing boiler and a tankless water heater. The air sealing points above are still worth considering in this case.
As always, this comes down to dollars. What do the various options cost? Will mini-splits with A/C command a higher price? In PA, they might. Gets hot and humid there. Also consider aesthetics and how that effects ARV. Getting rid of baseboard and/or radiators might be a big plus. Some people don't like the look of the internal mini-spit units (I don't mind them). There are in-ceiling options coming on the market, which are worth considering.
The energy savings are a potential selling point, but most buyers don't put a lot of weight to this (which I don't understand, but, you know, people). Selling the comfort of an efficient home can be a real win, though.
For more (way more) info, check out both Fine Homebuilding (their podcast is terrific) and Green Building Advisor.
