I'd probably only enter him in breed shows not general shows.
In any case, if you're new to showing yourself it's best to start in open shows rather than go straight to champ shows. GSDs are usually shown using a handler so perhaps speak to your breeder to find out which ones they're going to and maybe they'll take your pup in for you.
I don't mean to sound harsh, but how do you know you're pup shows promise? We all think our dogs are gorgeous

, but knowing what a judge wants is a different thing altogether. Also they change a lot from 5 months to adulthood.
Like I say, open shows are probably the way to start then you'd have a judge's opinion, just make sure you choose a breed specialist who likes the right type of dog