I have a 1948 1600 sqft two story double masonry house. The house has a two pipe steam system with copper finned radiators with no adjustments or valves. Contractors think it is a water system from the looks of the radiators. Not sure how old the boiler is but it looks like it went unserviced for about 10 years before I bought the house. When I had it cleaned they told me it was in terrible shape and to put a new one in for next season. The service man said it was the worst one he had EVER worked on.

Current radiator count-
First floor- 1 in kitchen, 1 in dining room, 2 in living room.
Second Floor- 1 in each bedroom (3) 1 in each bathroom (2)

I have natural gas in the house so I'd like to use that rather then oil. I have a new tankless gas hot water heater so the boiler will not be used for water. There is a small addition that uses electric which I'd like to convert over to run off the boiler. I have the walls open from a kitchen remodel to install the piping for the areas that use electric. The basement is unfinished so plenty of room to work. I understand there is a risk of water leaks from the conversion. Fortunately I am related to a plumber but I do not enjoy have my walls opened.

Let me know your thoughts and what to look for when I get estimates. I am open to any ideas at this point. I believe that no matter what I do I will see a savings in heating costs since the boiler is in such poor shape. Will all the pipes in the house need to be changed or just the basement?

Two main goals-

1. Heat the entire house with the boiler and remove all electric baseboard. This will add 1 radiator on the second floor, 1 or 2 on first floor and one in the basement bathroom.
2. Use natural gas rather then oil.