Seeing as you are open to spending the money on a whole new system and oil is currently close to $4.00/gallon why not go for broke and do it right.
Oil is terrible, dirty, inefficient heat and in my opinion should be out lawed as a home heating option. The have condensing boilers but I am not sure you can buy one in this country yet.
I would suggest you get a High Efficiency gas(natural or propane) fired condensing boiler. I have one and love it. Its capable of 98% efficiency and it only produces the amount of heat I need between 84,000 BTU's and 20,000 BTU's depending on the out side temperature. No sense in buring enough gas to make 84,000 BTU's when all I need on a 40 degreee day is 20'000. It also vents and gets its make up air through a 3" pvc pipe so there will be no need to rebuild your chimney unless you want to install a wood stove.
Tankless coils are quite possibly the worse way to produce hot water. Seeing as you are installing a new system why not upgrade to a better hot water solution. I would go with your idea of a closed loop system with an insulated tank. The only change I would make is to get a tank with a back up heat source either a dual coil ( from boiler) or electric. Super stor has many options
To do this right and save money you are going to need several pumps there is just no way to avoid it. My boiler came with all the controls I need for DHW and heating The only controller you would need would be for the solar side, I know FWWebb is now selling complete systems so you might want to look there
here is a link to my boiler