Here are some additional tips from a former mascot (Towson State University Tiger, 1987-88)
Absolutely include the cooling fan, or you will learn, as I did, that a fur and foam suit can send you very rapidly toward heatstroke even in an air-conditioned basketball arena (my university-issued Tiger suit lacked this feature).
You can put the view ports someplace besides the eyes if you want the mascot to be taller. The Tiger costume had white screens on the whisker pads instead of the eyes, which also provided some peripheral vision. However, I had a dead-center blind spot where the nose was. I worked around that by swaggering side-to-side whenever I walked, which people kind of expect a mascot to do anyway.
For more bulk, you can add football or lacrosse pads under the suit. The Tiger costume also had big foam paws to cover my shoes, but I don’t recommend that, as it limits your mobility.
If you’re a guy, wear a cup. Seriously. To the preschool demographic, you’re a giant stuffed animal. They’ll charge straight into you for a hug, slamming their foreheads you-know-where. A buddy of mine was the Baltimore Oriole the same year I was the Tiger, and he got a very painful injury that way. I learned from his experience and donned the armor.
You can add a tail to the suit, but be sure you have some wire in it as a stiffener so it doesn’t drag on the floor. Otherwise, you’ll always be tripping on it.
Wash the suit (and pads, if using) after every wearing. You will sweat profusely into it every time, and it will reek if you don’t clean it.
Have fun. A mascot suit is a license to make a complete &#^ of yourself in front of ten thousand people, with almost no accountability. I certainly took full advantage of that, and you should, too.