They can be already made, and anyone that has a decent amount of photoshop/imageready knowledge can do it... actually if they are already made the GS will do it for you in the request section opening on teh 10th of october.. (tomarrow)... but if they are not done already the GS asks that you only request us to make one minisig at a time..... or just animate multiple minisigs per request.
usually 5 is a good number, anymore and if you makle them fade the quality goes down... if it just switches from one to another with out a fade you can usually do more.. also using minisigs of the same size is USUALLY necessary.