its hard to say i had him for almost a year he ate like a champ and had a tank dedicated to him....i got him from a friend who also had him for a long time so its hard to say what went wrong.i do know that he slowly stopped coming out for food to the point where i couldnt entice him to eat even fresh crab(which he loved) im not even sure of their lifespan....mine was a g.smithi i would also feed him any live hermits or hitch hikers i could get from others or i found in my tank(as i hate crabs)
ive had a couple peacocks over the years but i found them very easy to take care of compared to the g.smithi
your crabs will probably be lunch when he gets bigger if you do set up a tank just for him use only one piece of liverock so you know where to find him come feeding time or if you dont see him in a long time
hahah makes me want to try another now hehehe
goodluck im sure youll do fine with him