The 743 falls nicely into the range that most attachments are sized for. It is becoming the de facto industry standard as SSQA (skidstter quick attach) for a lot of compact tractors as well, so there are a lot of companies providing things that can be shared. Chances are, most things that you'd find for sale will fit a 743.
As for what to look for: excessive smoke, does it start easy, seem to have plenty of power, doesn't leave puddles of fluid where it's sitting. Pivot pins are tight and show evidence of being greased, check for excessive slop in the linkages for the steer sticks and foot pedals. Does it turn equally in both directions, lift and tilt work smoothly with no excessive leaks in the cylinders. Pick up the front tires with the bucket and give them a shake, looking for excessive play in the drive chains or worn wheel bearings. I'm sure that Tazza and others who have them will be along with more suggestions shortly.