I have a Babylock Ellageo, Brother Innovis 4000D, and a Brother PR600II. Betty has given you great advice. If you don't want to spend a lot on additional software make sure the unit has a USB so you can take from computer directly to machine. There are some free viewer programs out there that will let you see the design and drag or copy to the USB. Allbrands.com has a free embroidery editor right now but I haven't tried it yet. The size frame I use the most is 5 x 7. I occasionally sew something bigger but not that often.
Buzz Explore is the program I bought to unzip, view and categorize my designs. I love it.