Using no one 30 or over the best possible team would have been:
Fox
Booker
Tatum
Brown
Bam
With a bench of Edwards/Mitchell/Ingram/Jackson/Haliburton
Maybe sub out Mitchell/Ingram for guys who are proven role players like Bridges/Gordon
Funny thing I have actually been thinking about this a lot over the past few days
PG - Ball, Haliburton, Fox
SG - Booker, Brown. Edwards
SF - Tatum, Bridges, Ingram
PF - Mobley, JJJ, Banchero
C - Embiid*, Adebayo, Allen
* I do see that Embiid has US citizenship and he is right now 29.
PG - Morant should be on this list but with his problems off the court I do not see them extending an offer. I like Ball starting because of his size and his 37% shooting from 3 will help. I was back and forth on Trae Young but again I can not dismiss what is said about him. Haliburton could also start with his shooting. Fox is just the perfect change of speed type of backup.
SG - Booker is the guy hands down and should be on the roster. Brown with his defense is also needed. Ant has shown he deserves to be there. Jamal Murray is also an option as is DM but I have these 3 rated in front of those 2.
SF - Tatum is the best SF in the NBA right now. Bridges has shown he belongs and his defense is greatly needed. Ingram is the one I went back and forth on as he is super soft. His size does create a nice mismatch but he didn't do great on the team this year. Scottie Barnes is a nice and upcoming player who could fit well here. Devin Vassell is also intriguing.
PF - This was the hardest of the positions to figure. I really like JJJ starting but I had Mobley start for his defense and switchability with the Euro bigs. I had Randle rated pretty high I just do not like his defense and if you keep Banchero on the US roster that will keep him away from the Italians. Zion has to be mentioned here but I figure he will be injured again so would not be able to play. He could have a place on the US roster if he was healthy.
C - You can see my asterisk for Embiid but Adebayo and Allen are solid backups that can play with Euro bigs. If Embiid is not healthy then go with Wendell Carter or Robert Williams. I like Kessler too if he is used and will make practice easier as he can play that bruising big.