We were also really concerned about what we'd find under the old siding. There was a bit of rot here and there (remember the already replaced joist in one bedroom?). But it ended up not being as bad as we feared -- except for one kitchen window. Yes, the one right in front of the recently finished counter & sink. It involved a window removal with some replaced framing and drywall.
As the project dragged on, the contractors got sloppy and quality went downhill. I can still see their mistakes. But overall we lived with the outcome and were just relieved when it was over.
The new siding was primed so we decided to wait on the paint for the time being. Perhaps another DIY project? Maybe so and maybe not.