Justin it is acceptable to do what you like.
For me the fieldset is about grouping fields, ie a set, together. So I would be inclined to group fields in one or more groups or as a lable in some cases. I would also put a space at the begining and end of the legend. Inputs like tags and select widgets stand alone to me and I dont need to clutter the page with additional visual infomration unless it adds value and meaning.
However if you have looked at the Field Editor cascade? This only works to customise the edit component and is used by the edit template to produce custom edits for a given field. It may make sence to try and reuse this mechanisium then build your form on top of that. Thus if you have more than one form the edit component need only be modified in one place.
- I am yet to do this myself but will soon given my work over here [Proposal] Updating field handling functionality in TiddlyWiki
- Modifying both edit mode and forms used in view templates to edit fields is on my roadmap.