I have 2 Brothers, a 3000 which takes floppies and the Brother card, and a 4000 which uses the card or a usb. It also connects to my computer to receive designs. Using floppies is soooo slow, both to put designs onto it [you can fit about 10 designs on - about 1.40mb- depending on the no. of stitches ] and loading into the machine. All designs have to load to the machine, you can't just select one from the floppy or usb. I think some really expensive machines can do this. Also, with a bit of age, the computer has problems recognising the disc contents. They are also getting scarcer in my towns. Usb's are the best invention in ages.
I use Buzz Explore for viewing thumbnails and printing templates, changing colours etc, and for digitizing I have Generations. Heard good reports about Embird for digitising, and believe it's less expensive. If you buy 2nd hand ask if the seller has the software as well. Often new machines have the software included as a deal. My Brothers are very user friendly, I've never had to ask for help to work things out.
Best of luck