I think you finally stumped the panel. I really don't have any solution for your question. You are somehow trying to track a series of Tasks. Since nothing is "closed" out at any point, we do not have a way to do that. Usually people just work on something until it is done. I would think that you would just bill your work, whatever it is on some regular basis (e.g. weekly, bi-weekly, monthly, etc.). When you Invoice, it would just pull any new entries.
You can make items "hidden", such as Clients, Projects, Tasks if you do not want to see them any more on the picker lists. They will always show up in the database maintenance screens.
As for your questions about Editing. We only allow editing from the Setup -> Database section. While you can add things on the fly from Entries, you cannot edit them. You should not have to be editing records all the time, if ever, after adding them.
I guess I do not have an understanding of how you work as it sounds very different than regular Time Tracking.
You can "turn off" many of the fields from printing on the invoice by going into the Setup -> Invoicing -> Export -> Description Fields and turning them Off. That would allow you to put a short note in the Task for your own info, without displaying it on ever line of the invoice. However we probably would not be adding any large multiline text box in the database items. I will add it to our "wishlist", but can make no promises.