Whether it's a dealer or private purchase, make sure that they take the time to go through everything with you and help make sure that you're hitched up and checked properly, that you've got your extender mirrors adjusted correctly and that the caravan lights are working correctly.
When you set off, you'll be surprised that it is easier to get moving than you perhaps expect, and keep telling yourself 'remember that I'm wide'. Take quite a slow, wide line around corners, but you can see in your mirrors how close you are to the kerb and get used to where you need to be. Once you've got accustomed to it, you won't always be massively aware of any feeling that you are towing, but do stay below 55mph until you feel comfortable and genuinely capable.
My experience is that 95% of other road users are generous towards you, giving you space and so on. Just occasionally, you'll come across someone who makes life difficult, but just be relaxed about it.
Using the motor mover is easy peasy. The only thing you're likely to get wrong is forgetting to release the handbrake (or apply it) before and after.