Keep your old characters, you've got quite a few slots you can use now and you should try every class at least once to see if you like it (and enjoy the story! Roll Agent!)
^ This (And on my 2nd Agent. Yeah, story is that good).
If you get into crafting your own gear or running missions for stuff for your other toons, making $ on the market, etc. they could be handy.
If not, you can always delete them later.