From what you are discribing, it doesn't sound like 1" pipe to heat the house is going to cut it. The pipe size is determined by, how long the pipe run is in that zone and how many BTU's you would like to deliver to that zone.
Read this http://s3.supplyhouse.com/manuals/13505 ... D_FILE.pdf
It is the "Taco Radiant Made Easy Application Guide" The BTU output listed on your current oil furnace is a good number to use for the Q factor. You can plug different pipe sizes into the formula to see how it effects your pump size. Very generaly, you can use a smaller size pipe BUT, you then need a larger and more expensive pump to get the heat where it needs to go. The bigger pump also uses more electricity, therefore costing even more.
My guess would be that you need 1.25" or 1.5" pipe for the house zone. Don't forget the PEX pipe needs to be oxigen barrier pipe, you don't want oxygen in the boiler water, it will rust the innerds of your nice little EFM. The pipe also needs to be insulated, http://www.badgerinsulatedpipe.com/
is a good place to get pipe from, nice people and I think price wise are the best. Central Boiler also sells very good insulated PEX.
You should also think about heating domestic water with your EFM. If it doesn't have a domestic hot water coil, get one.