Custom Fields and System Objects?

Hi all,

Setting up MT5 in prep for migrating from 4.3, and digging into the custom fields I've been wanting to use for some time. Most, such as the category sort#, book info, etc. are going in at the System level for cross-blog access.

My question/problem is that there are several fields which I could easily see tapping across pages, entries, or even assets within a blog--like a category/folder sort#.

Is it possible to accommodate that kind of flexibility within MT's constraints of assigning to a specific System Object + unique Basename? In a remotely efficient way--i.e. without ending up with _e, _p, _a dupes that would fragment the data, forcing me to code endless "or"s into my templates to meld everything back together, as well as periodically houseclean ;-).

BTW, what exactly does the System Object assignment mean at the UI and DB level? (Vague perceptions of form appearances, but docs are beyond sparse.)

Thanks for any info or best practices!

Ann