Can't wait to see him!
The backstory works, I guess, although there already is a Makuta mask maker and a couple Makuta who specialized on mechanical stuff - but there isn't any reason why Raximoras shouldn't do something like this, too.
I like the idea of him doing armor repairs (probably with the help of Nynrah ghosts from time to time?) and he can also be an architect, if you want, but the place for the physcian (like in before they evolved) is currently already reserved, so I would ask you to not include that.
As long as the MOC looks good there probably can't be a "too big", although you should try to make the MOC not taller than those 1&1/2 feet.
Have you read the updated rules in post 829?
I'll put you on the list for a male Makuta then.
Updated list is in post 829
Rules can be found in post 829 and additions in post 1
Currently there are no more Makuta to be assigned