You will not be whitelisted as NHS or Police because you need to do an application and pass all of the relevant tests for it. There is no whitelisting for civilian, so join as many times as you want. But we don't do Public Slots here, so you have to work hard to get your whitelisting!
Yea just make sure you click on the purple square on the left hand side and choose an empty slot, then you will be good to go, and welcome to the community. If you need any more help join the TeamSpeak and ask for help I'm sure you will get it