We have a really good team for a one year run. As the OP says, after that things get dicey for sure.
I think we are going to be right in there with Toronto, Washington and maybe Milwaukee (there is usually one surprise team) and we may well get another shot at putting a scare into Cleveland.
I believe that Horford will get traded, just not sure when, and I don't see how we can sign Thomas to a max deal. We would be a repeat offender of the luxury tax unless we traded Horford for nearly all expiring contracts.