5-6 years machine is good.
As for embroidery software, they use their own language/format. So if you have a design in Corel/Illustrator, you will need a digitizing program to do it or get someone to do it.(
http://www.wilcom.com/,
http://www.wingsxpsoftware.com/)
As for what to look out for:
1. Look at the room it was used in (humidity, dusty, heat). We run our machines in an air conditioned room to keep the embroidery computer system cool and dry. It cost a lot to replace one of those things. We also dust once a week.
2. Do a test run on the head to check if it can do good smooth simple stitch. Then check it by looking on the back of the embroidery. It should be smooth and straight.
3. Hoops has to be well maintained as stated by GraphicsDisorder.
4. USB is better than floppy, we converted all our floppy to USB. It is faster and cheaper to handle.