Can I use both roles: Requester and Helper on the same account?

Yes. These are two modes of the app, and each user can play the both roles. In other words, if you use the Requester mode and you post a request, you considered to be Requester. If you are locking other user’s request for offering some help, you considered as Helper. The app provides a button to switch between modes.  The only thing to remember is that when you play as Requester, you see your Requests. If you play as Helper, you see requests made by other users. It might be confusing at first, but easy to get used to.