Ron,
If it is going through the same developmental stage that my scarlet-chested is, and that my bourkes also went through, it may be very timid at 5 months of age. I would suspect that treating it just the way you treat Twitter would work wonderfully if it is in this stage. I wouldn't rule it out if it is skittish right now, because my Isaac was highly outgoing, came to anyone in the bird store, adult or child, and came to all of us when he first came home, until he reached some where between three and four months of age. We also took him to the school to visit, and he went to every kid in the class.
I don't know if my daughter scared him one day or if flying into a wall and sliding down behind a couch scared him or if he just hit a normal developmental stage, but he became highly skittish, overnight it seemed. I tend to think, though, it is as much developmental as anything, and maybe it was also bad timing that he got spooked just then. So many species of parrots go through skittish stages when they would be learning to completely fend for themselves in the wild, and I really think grasskeets probably have such a stage, but we don't have anyone writing books on their normal development the way we have people studying and writing about the more popular pet species.
Bourkes, if they have such a stage, would naturally tend to freeze more at this time, because they are well camaflouged (sp? sorry, absolutely no clue on the spelling of that, lol). I suspect you have experienced that with Twitter. Scarlet-chesteds would tend to flee, maybe moreso the males than the females, because they are brightly colored.
I guess all I'm trying to say is that I've met a hand full of scarlet-chesteds who were handfed. That isn't many, but they all were very sweet birds. 5 months of age seems to be a frightening time for them. I also think that a scarlet-chested kept with budgies might be a bit nervous due to that - not bad, and nothing to cause any lasting emotional stress, but the bird will be happier once you put it in your quieter home with its own cage and your other sweet birds for company.
I agree that it will be nice for the two birds to be of opposite sexes, and you will probably be happy you have two cages. That way, if they want to visit one another, they can, but they can also have their own space.
Congratulations on finding a hand-fed scarlet chested male. Because you enjoy Twitter, I really believe you will enjoy this fellow, too.