Congrats on your new-to-be birdie! That's great you'll be getting a second cage, so you're on the right track.

I would recommend keeping the new bird in quarantine for a month or so. This means to refrain from introducing them to each other for that time, and keep them in seperate rooms. That way you will have time to get accustomed to the new bird's habits and reactions, and you will also have time to find out if everything is ok with the new bird (healthwise and behaviorwise). It is always recommended to quarantine new birds before introducing them to their friend. After the quarantine period, the birds should be used to hearing each other's noises and sounds, so they'll be aware there's "someone" in the house, and they'll be somewhat prepared. Move the new bird to your Tweety's room, and put new birdie's cage near or next to her's. Let them get to know each other from different cages before letting them out to play together. Once you feel they are used to each other's presence, let them out for playtime together, but keep a close watch on them. Don't put the new bird in Tweety's cage because she may feel he's an intruder in her territory and try to hurt him. Let them get used to each other by playing outside the cage, under supervision. After they get used to each other and you are sure they will not hurt each other, you can try to house them in the same cage (if that's what you are planning to do) otherwise, they can live in their own cages but have playtime together outside the cage everyday. Good luck and be sure to post pics!