As Sawtooth mentioned, they use outserts. The stainless actually bend more than the aluminums in hard hits. The outsert by Firenock is much better, IMO.
400 spine will work great with your 55# set-up. If you read my earlier reply, you will see that I shoot them in bows from 50# - 60#'s. I pull just a tad over 29" and keep mine cut to 30" before insert.
Penetrate like crazy!
As far as fletching - 5" is not better, although you can use it - a little tight if you use a really tight helical. 4" works great, and if you are using a heavy point you can likely get by with even smaller.
My set-ups with AeroOutsert and 300 grain point weigh 560 grains and are 27% FOC. Fly great even at 40-45 yards. Hit like a sledgehammer! With the stainless rod footing that I mention above, I drop down to 275 grains up front for same effect, but one heck of a stumping arrow!