first of all congratulations if you do end up getting another bird!
I don't know much about budgies, but with cockatiels you have to keep the new bird in quarantine from your other bird for four weeks, or until he sees an Avian vet. When I got Austin we took him to the vet the day after we got him and he checked out fine so we put him in with Lachie straight away (in a new cage though - it's probably not a good idea to introduce the new bird into old bird's cage, because of territory issues).
Even when they're being quarantined the birds will get to know each other, because they'll sing and call out to each other.
And by the way...I'm no expert on any of this! These are just tips i picked up when I got Austin. Popcornbird is probably the person you want to consult for a definitive answer though.
I hope they get along, and your new birdie brings you lots of joy! Good luck!