Questions regarding instillation of Burnham IN4 gas boiler

Hi, I'm an having a new gas boiler installed (Burnham Independence IN4) and there have been some discrepancies between plumbers about instillation. So I'm wondering if anyone can help clear things up. *1)* Do you use only one of the supplies and have one riser or use both and have two risers? *2)* Should the header be a larger pipe size than the riser? One said for this size boiler it doesn't matter. *3)* I've heard the piping should include a drop header design while others have said there is enough room to go up as high as needed so we don't need to have a drop header. Thoughts and if we can go up as high as needed to not need a drop header, how high should that be?