First, kudos for looking to make your observation/feedback process into a conversation through the use of a collaborative tool such as gDocs. It just makes sense!
Second, WRT the time issue, perhaps the more-visits/more-feedback balance may vary by teacher, and you may arrive at a more comfortable spot with this as your process evolves and the conversations with teachers deepen? I think it would be truly telling to see how the results of your observation/feedback/conversation process unfold over an extended period of time. Tenacity on your part in making the time will be a key.
Finally, have you considered trying a gDocs-accessing iPad app like Office2 HD or QuickOffice? They allow you to edit an existing gDocs spreadsheet, albeit through a stardard formula bar interface. Another option would be to forego the form and simply duplicate an existing doc template in a shared folder of gDoc documents, giving you the format/flex of a word processor with the sharing capability that gDocs provides. Other options exist, but the open form and share ability of gDocs seem to be keys in your process.
