Hi,
1. Do I have to design a login screen for my application?-It depends on your customer requirement. For Custom Login page for SAPUI5 apps, please refer :Login page for custom sapui5 applications
Note:if you planned to run your application as a stand-alone application(accessing app using direct URL), then it is recommened to have custom login page, otherwise if the aplication will run along with other applications in EP portal then login page not required(as EP portal will already have a login page)
2. If yes, then how do I handle user logins? How to handle user authentication for users created in NW Administration?-The class that you are going to assign ( as mentioned in the above URL) will take care of user authentication
3. After the successful login, I have 10 links on my landing page. How to achieve role based authorizations for these links?- If you are looking for a programmatic option, you can create a common oData service, which handles the authentication based on role and return a parameter which gives the runtime decision to show links on application.
Hope this would be usefuel!
Regards,
Meganadhan S