I'm with several here. I select the broadhead I want to hunt with. Then I tune the arrow by spine selection, shaft length, and insert weight.
I select my broadhead based upon trade-offs. It must be a broadhead I think will give me pass-through penetration out of the bows I hunt with. Too-wide a broadhead, or too many blades may impede penetration.
For example, the broadhead I like these days is a single bevel 2-blade. I can get it in 100, 125, and 155 grains. I had good luck in 2010 with the 100 grain (and insert weight). This year I used the 125 grain to get a bit more broadhead width. I changed my arrow spine and insert weight to make it work.
I was toying with going to the 155 grain version this coming season but have decided, because it is a bit wider, I might not like the penetration.
The field tip, is the least important consideration. You can generally find or modify with weights a field tip to replicate your broadhead arrow. If I couldn't, I'd practice only with the broadheads.