Hi Leon,
You've got a good machine and yes there is a steep learning curve.
Couple of ideas I recommend, one already mentioned is turn off the icloud if it is on as this copies everything from your iPad to the internet and has the capacity to download it all again on a restore from the icloud and that includes any pictures so if you accidentally restore from the cloud then it'll use heaps of download.
I recommend you do your backup to your lappy with itunes and you can restore from there without using any of your download so you can add and remove pictures without worry.
I personally haven't tried syncing with my iPhone, haven't found the need.
Downloading updates for the operating system eg iOS 5 to iOS 6 is big and will use a fair amount of your limit but they are generally worth doing.
Updates for apps can be as little as three or four Meg to things like Starwalk or Solarwalk are large at around up to 150 Meg so they vary a lot and iTunes will tell you how big they are before you start to download from the net so once you,re setup they aren't too bad but having said all that you may well have to consider paying for more down load allowance, I guess it'll all depend on your surfing habits.
Hope this helps
Cheers.