Rule of thumb for owning a mantis, only put things in the tank that you don't mind loosing. They are predators and if the opportunity presents itself they will hunt. I think a hardy open water swimmer like a chromis/damsel and lots of cool macros is how I'd go for this tank.
Edit: being that this is your first sw
tank I thought I'd lay out what I think would be a good plan after the cycle. Get a fish (blue reef chromis would be my personal recxonendation, bold personality, active, and tough) and let him stabilize your tank for 5-6 months before you add the mantis. During this time you should focus on getting the basics of sw
down, mixing water, matching params, maintaining stable params/element levels as mantis are very sensitive to swings in water. Decide wether you want to just go rocks or add corals/macros (again nothing you'd mind loosing because the mantis will re-decorate for you :p) and get them where your happy before you introduce the mantis (wouldn't want to put my hands in mantis tanks very often). And then go get the star of the tank