I did try to find the awning size for you but cannot find the details for that year. The simple way to get the size is to run a length of cord through the awning rail starting at the ground one end and ending at the ground at the other.
If you want a porch awning check that the width will allow the rear end to go between the two windows or cover both. You should try to avoid the end crossing the window although we have managed to work with that. They do have the advantage in that if you change the caravan, the awning should still fit, which is less likely with a full one.
As for the make you buy this depends more on your budget. Basically you get what you pay for and the higher priced makes are generally far better. The cheapest ones can have a very limited life span.