"Cold Start"???
Is this boiler even able to condense? It's oil fired right? I don't think allowing the boiler to come on only for DHW would be wise as it would cause your boiler to condensate for which it is not designed. Maintaining a 140 degree boiler loop temp is crucial for equipment protection. If you want to cut energy costs, have your combustion checked with an analyzer along with a good cleaning if you haven't already done so. Around here our #2 fuel oil can vary in blend according to the season, so it is common to have anything oil fired checked out at least twice a year during the season change. Another option is to have the boiler "isolated" from the rest of the system with some electric zoning valves. So if there is no call for heat nor DHW, the valves could isolate the boiler loop and allow it to maintain 140 degrees without heating up a lot of water unnecessarily. Beenthere is on the money, the indirects sized properly will be fine for 2 people and many more. Again, proper installation is critical. Bear in mind that when you go indirect, an outdoor reset is no longer used.