Lots of different opinions on this one, but I'd say start small with the cleanup crew and grow it along with your fish. No more than 2 or 3 nassarius snails, maybe 1 turbo or an astrea. I'm a fan of hermits, but get some shells to give other options than them killing snails. Don't be afraid to feed a little extra to keep the crabs fed in the beginning. Another easy and fun fish for a new tank is always the firefish. I'll always have one of those in my tanks.
If you're set on getting a six-line, add it last and know you'll never be able to have another wrasse in that tank as long as the six is there. I just gave my little murderer back to the store. They're smart, quick and hide in the hardest to reach crevices, so once it's in, you'll only have about a 50-50 chance of catching it with a bottle trap later on.