Only tips i can give you is what i learned when i bought mine.
I have a bernina 180 artista which i like BUT i bought mine secondhand and did not get any lessons included so cannot use my machine yet to its fullest potential. Lesson one get lessons so you can use your machine and your potential creativity to its fullest and buy new if you can afford it.
Lesson two look at top end machines and try them out to see what features they have and then look at middle and bottom end ones and try them out to see which features you like. Go home and work out what features you need and dont need. Ie stitch regulator might be a good idea if you are thinking of stippling etc Do you want the bobbin thread case on the side or top...thread cutter etc..electronic or not
Lesson three check out the machine throat as some machines have a really big throat so you can fit your whole quilt under there without having to fight it the whole time you are quilting.
Lesson four check what feet your machine comes with and what you can get thrown in for free BEFORE you have told salesperson you are going to buy..
Lesson four buy your machine from a dealer that is reasonably close to where you live for ease of repairs and advice and bits and pieces.
Lesson five buy from a dealer that you like and is helpful right from the start..Ask how much to service the machine..electronic ones can be expensive..
Thats all i can think of..happy sewing machine hunting! Let me know how you go