Shorter skis for teaching beginners and intermediates is a good idea.
You'll find yourself doing a lot of kick-turns, stepping around, skating, side-stepping and all manner of quick-footed antics to get around your students and help them get around. Short skis support this more easily than longer skis and they maneuver in tight spaces easier as well.
It's best to select ski-types that mirror what your students are likely to be on. If you'll be teaching Alpine beginners (likely for a new Alpine instructor) you'll want to avoid fat skis, reverse-camber skis, telemark bindings and such. It's important that your skis perform similar to the way your student's skis will perform since technique and movement Demos are so very important to students.
Top Sheets are also to be considered. New skiers (especially kids) will frequently ski right over the top of your skis cutting deep gouges into the top sheet. It's painful to watch/feel. More-so if you have skis with graphics you really like!
Turned-up tails are great for skiing backward in front of students - but be aware that anyone skiing onto your tails will likely get stuck there (trapped by the upturned tail) and they'll slice their edges back and forth struggling to get disentangled......
( I find two-part marine epoxy works well to fill in the gouges.)
You might even consider going to a swap meet and picking up a pair of inexpensive used skis for teaching.