I like using Float & Thermostatic traps these days, they are good at removing air that you will have on start-up. You could use a 3/4" or 1" F&T-125 trap. Make sure you get the orifice for 125 psi steam.
I have seen some large traps on the main headers for boiler, these are there in case there is carry-over of boiler water into the steam line. I don't usually recommend them but prefer to prevent carry-over at all costs.