That sounds good to me. I'm convinced that there are nice benefits to the restriction, and I also don't think it's hard to work around it.
This sounds great to me. I could see us perhaps wanting to split this into two options at some point (someone might want to remove a lengthy form name but keep group names). However, I wouldn't be surprised if most users who are interested in these options would want to remove both the form name and group names.
This seems like a nice solution to me. Given how many users use XLSForms, I would think that duplicate names should be relatively rare.
By the way, @notaplatypus, I'm not sure whether this would be helpful, but I believe it's possible in Google Sheets to automatically resize all columns at once: select the entire sheet (you can use the select all keyboard shortcut), then double-click the divider between the A and B columns toward the top. The columns might end up wider than ideal, but at least all column headers will be visible without much manual effort. (Or is it not possible to edit a Collect Google sheet in this way?)