I wouldn't prioritise a trigger as an immediate upgrade for an Ion. The stock one aint that bad!
I disagree. I've had 2 Ions so far, got a mates one sat right here and on all three the trigger's were/are poor!
If you are serious about shooting your gun with any degree of speed ROF-wise then a new trigger is a necessity.
QEVs are fine, but not a priority IMHO, the gun will shoot just fine without one, the same could be said about bolts too.
The stock duckbill bottomline is uncomfortable for most, so that needs near-immediate replacement for some people.
A new clamping feedneck is handy, but the stock one will fit a number of loaders just fine.
Personally, I wouldn't go much further upgrading an Ion, you can buy superior guns for the same cost in the long run. I say do the basics, get it rolling, get playing with it, save the cash and move up the marker ladder.
But that's just me!