Hello I'm a new guy but I used to work on Glocks all the time. The lone wolf trigger kit is great and so is the Ghost Rocket kit. If you are going to mount a red dot system you can cowitness with your iron sights to help with finding the dot faster. It requires the slide to be milled but its a great setup and if the dot dies you still have sights to finish you hunt.

heres a link to what it could look like. They do G21's
http://tsdcombatsystems.com/tsd-red-dot-glock-pistols/tsdglockonarock/

What ever you do enjoy it or its not worth it