I am new to using Wix, but I have been able to install my windows service fine what has no UI prompts currently, but I have now been asked to allow custom installations. What I mean by this is they want us to prompt the customer for a text entry like company name, and then we use this in the install directory e.g. C:\Program Files (x86)\MyApplication\Company Name and also for the Windows service to have this e.g. MyApplicationWindowsService – Company Name.
It's vary big and general question. I suggest you to start with some tutorials on how to customize the UI.
For Example: Tutorial 1, Tutorial 2.
After trying to implement your customize UI with no luck, you can post a new question with specific details and your snippet code.