Edit > Preferences > Always check for Available downloads.
Edit > Preferences > Automatic downloads. Then uncheck Music, Apps, Books if you do not want them downloading automatically.
None of this really has anything to do with syncing but rather what gets downloaded automatically in iTunes.
If you do not want new apps syncing to the device on a sync session, with the device connected, go to the Apps tab and uncheck the option for "Automatically sync new apps". This must be done for each device.
I live whaer I don't get the super fast internet its snail speed so to do more than one is a pain.
This has nothing to do with syncing. I believe you are confusing multiple processes.