I'm not overly concerned about the rookies.
Thomas, Horford, Hayward, Morris, Crowder, and Baynes are all vets. Smart is basically a vet, heading into his 4th season with over 6,600 NBA minutes under his belt. Those 7 guys are likely going to make up the regular rotation with Brown, Rozier, and Tatum. So yes, there are going to be a lot of young guys vying for minutes but they'll be end-of-the-bench minutes.
As long as Brad incentivizes smart, team-oriented play with minutes, they'll be fine.