A pretty good expectation for number of inputs is something like 6-10, with a likely average of 8.  The number of inputs will equal the number of outputs and the number of outputs can be estimated from the observation that a typical transaction will have one recipient and one change. Each of those recipients will receive an amount that will probably have between 3 and 5 significant digits. It could possibly be smaller; many retail items are priced with one or two significant digits (29.95 is actually 30.00, or one significant figure; 14.95 is 15.00, or two digits; etc.).

MOD NOTE: Lets cut short the back and forth on bytes, kilobytes, etc.