Can I in the meantime install the free version, and do whatever settings, install a couple of docks,
and then when I push the purchase through simply update from the free to the Plus version?
You can,but you will need to uninstall the free version before installing Plus.If you decide to use the free version,save your dock(s) you create and you can reload them with OD+.Just select the Themes tab in Plus,"Load Previous Dock" and your saved docks will be listed.
You won't lose them or any icons ,backgrounds,etc. that you download.They will be in Username/Documents/Stardock/ObjectDock Library.
Edit: I read LanTecs reply so I should add that you should save the "Backed Up Themes" folder somewhere to make sure they aren't deleted. It's up to you on waiting or not,but it may be easier to hold off on it. I lost some docklets which I had to redownload and it reset my weather icons back to default. No big deal.Otherwise the upgrade went well.