I recently purchased the 5.0. I was about to purchase the 3.0 new from a shop when I hesitated they offered the 5.0 that was used. I took the chance and have a beautiful machine. I like the larger harp and the bright light. The learning curve for basic sewing was quick. Some of the specialty stitches...well, I will never use. I got a needle down feature, and a feature that helps with more even stitches when quilting. It is not a stitch regulator but mimics one to an extent. I like the machine. It is quiet and so far a good purchase. One down side, there is always one, is the machine is heavy for me to carry about. This is not the machine I would take to a retreat just because of the weight. For you this may not be an issue. Make sure the second hand machine has a good basic selection of feet including a quilting foot or two. They are pricey and check that the machine comes with the users manual. Little things but ones that will keep you from frustration.
One thing to consider is if you have a local repair shop that will work on Pfaff. It is my understanding that the 3.0 is no longer being produced. Now that does now mean it is a poor machine only that the others models have more bells and whistles. But you do want to know if there is a shop to get replacement parts, extra special feet, bobbins (can use Viking bobbins). Happy machine shopping. It is a BIG decision.