I had to install 5 first (get new disks from EQ because I couldn't find mine), then 6 and then 7. Couldn't skip a step since all were upgrades. I started with 3 or 4 and have upgraded each time there is a new version out.
EQ5 is great as a standalone program and a learning program. No, you wouldn't be able to reregister it in your name if you bought used and wouldn't be able to upgrade from it. But, I still think it is the best program for quilting design out there. Probably would think 7 is best if I had time to really learn it. Anyway, all three are on my computer and are working just fine. I recommend you spend the money and buy whichever version you can and enjoy it.