I have two cockatiels and, at the moment, 11 budgies who are either mine or who I am fostering for a rescue. I had one cockatiel (Simon) and several budgies (fosters) before getting the second cockatiel.
Simon likes having other birds around and made friends with a couple of the budgies before I got a second cockatiel. Now, he sort of regards them as pests, but pests who he likes to boss around. The budgies for the most part ignore him, except for two who will stand their ground and have been known to grab at his tail in retaliation. I do let them out at the same time, but if any of the personalities were even a touch more combative, I wouldn't be able to.
I would say that there is no knowing what would happen. As another poster said, hand raised is no guarantee of what the cockatiel will want as s/he grows up; there's also no knowing how the budgies and the cockatiel would interact. It could be great, but you would have to be prepared for a wide variety of outcomes, even, "well, this didn't work out well" and re-homing the cockatiel.
On the difference between having a cockatiel and budgies: in my experience, the budgies are perfectly happy to on with their chirpy little existence without me when I'm busy. The cockatiels, on the other hand, are a bit more demanding
. Some of them can be quite loud about it. Their poop also makes a much bigger plop and they generate a lot more dander
I do love my cockatiels all the same.