Use Case

I have a requirement where user can add an item to the database and if they want, they may modify or delete the item from databse. In this case shall i write one use case for 3 types (add, delete, modify) of operation and put modify/delete options in the "alternative flow" or i need to write 3 use cases for 3 types (add, delete, modify) of operation? i have opinions from people for both cases. But which one would be actual format?

RUP project planning

RUP has 4 phases and the project has to go through that phases. But when i am planning the project i have to give an estimated time to complete the project. RUP says to plan for the next phase in the current phase. in this scenario how can plan for the whole project. If i use UCP method to estimate time, i have to have use cases written. At the initial phase (inception), i don't have use cases written. is there any efficient method to estimate time or i have misunderstood RUP?