Reaper or wait?
If you want to play the reaper you can start with unlock some skills and traits, then you can play as you want. If you want to play that build still without all the traits and skills you can do without so much problems.
just have fun :-)
Casually? Go for it!! Reaper was one of the classes that I was ready to jump right into when I saw the Elite Specs being promoted at the time. It’s a really fun class and gives you the “Reaper of Death” feel. You’ll unlock more of the Spec as you go, but otherwise you can play around with it.
However, if you plan to do anything with a group (dungeons, fractals, etc)? You’ll want to check in with the other folks out of courtesy and let them know you’re bringing an incomplete class.