In less than a minute, Vincent had answered my questions!

I figured I'd share the answers in case they're helpful to anyone else:

1) Yes, you can run the sync program only - with no need for our email services at all.
2) Yes, [email is still handled independently via BlackberryInternetService]
3) Nope, [no data size limits at all]
4) Calendar sync: Date range is 1 month prior to 6 months ahead - but unlike Google, we *do not* delete anything that is not within the range. We just leave it and the window changes automatically. Recurring calendar items are not an issue at all!

(ThinkPost may not be exactly the right solution for my company president [it's not 100% seamless and invisible...] but I may implement it for my other users, as it sounds fantastic. I'll certainly update this post with any feedback I can share.)