Just a quick update. This week will be busy so I don't anticipate too much progress. I did get the axels mounted though with the wheels on loose. This will let me adjust as need as I add track links:
Following my own advice I ordered lego rims for the road wheels and drive sprocket, way cheaper than casting them myself and easier to work with too.
The turret is built as simply as possible, with a washer added for reinforcement: