Ok, never owned a crossbow but I've finally decided to get my first crossbow   Lots of research narrowed it down to the excalibur matrix 380 or Micro.  I'll go with the micro.
Here's my question.  The arrow weight is supposed to be 350 gr with a 150 excalibur bolt cutter broad head  and 16.5" long (package deal).  What happens if I use a shorter or longer bolt or a lighter/heavier bolt?  I assume lighter gets better velocity, so what if I went 50 or so grain liter? Would that be a big deal?

Also, does anyone recommend a good bolt/broad head combo for use with this setup?  Thanks for the help

Late to the party and I'm sure you're squared away, but you don't want to go under 350grns total arrow weight with the micro.  

As long as you make that weight, I know folks who run all the way down to 15" bolts with them.  

For me, I use 16.5" BEES with 110grn brass insert and 100grn ramcats for a total weight right below 400grns

If you go lighter than 350 you will risk a partial dry fire a could damage your limbs.