A ‘b-condition’ restricted licence only enables the driver to operate auto and synchromesh transmission type vehicles that correspond with the class of licence they currently have.
It depends what sort of trucks you are likely to be driving and in what type of transport industry you are venturing into. For example, If you are looking at driving buses or working for your local council, then an unrestricted licence would not likely be required. If you were looking at wanting to drive American trucks or working in the civil industry, then you are likely to require an unrestricted licence.
No you don’t. The only time you will need to go back to the RMS is when you take your certificate of competency to them to get your licence endorsed
You will not lose your unrestricted licence.