What I have done is make a list, similar to the things you have listed above, and take a road trip to local dealers....make a commitment to yourself that you aren't going to buy a machine until you have visited "X" number of shops and thought about it. With list of things you want in a quilting machine go looking. You will learn something new at each shop and you will find the machine and the deal that best suits your needs.
Some additional things to consider adding to your list:
Service - Do they do their own servicing and are they a factory authorized sales and service center?
Classes - Do they offer classes with the machine, how many and for what duration?
Financing - If it is more than you want to pay right now, is financing an option? Many are offering 0% for 6 months to encourage larger purchasing....
Purpose - Are you going to be using it for just your own pleasure, or are you hoping to go into business to earn additional income or even just support your habit?
Good luck!