If you are going to add a basslet, I would advise a Swalesi or Swissguard. I have the latter and it's awesome. Eats like a pig, has amazing color and doesn't bother anyone. Both are quite $$$ but worth every penny. You don't see them often in the aquaria.
For a tank that size I would go with a tailspot blenny. It's a nice and funny fish that reaches about 2 inches. Lawnmowers get huge.
Six lines are pretty. I had one. She was mean to fish that I tried adding after her. I took her out. So I would add it last if you end up getting one.
Jawfish is a cool fish. I wish I had one but my sand bed is not deep enough.
As far as mixing fish it could be hard to say. I think firefish and watchman goby should be fine. Gramma and jawfish could harass gobies. Jawfish can also cover your corals with sand. If you don't dust them off you might as well say good bye because it will die...unless your flow takes care of it.
