To properly size it we need the btu rating of your boiler, water heater, dryer and stove. The dryer and stove I could get close guessing, the boiler and water heater are the variable. We also need to know the distance to your furthest fixture and how many elbows and 45s you have. Then the distances to everything branching off, again with the number of fittings in each branch. If you can't Tell the number of fittings then you estimate it as 1.5x the distance.
Taking a guess here. Your meter is probably right outside the boiler room. You will need to bring at least 1", probably 1-1/4" into your house from the meter, Tee off that 1-1/4" to feed the boiler and water heater then continue on in 3/4 to the stove and dryer Can't say anything for sure without all the information though. Are you from Long Island, NY? If so what type of pipe are you using? Most if not all of Long Island requires black steel pipe for gas inside. I know you can buy csst but it's not code.
Here is the sizing table. http://www.engineeringtoolbox.com/natural-gas-pipe-sizing-d_826.html