(section: 2 / paragraph: d / line: 1)
Yes, you may bring a music stand.
(section: 3 / paragraph: b / line: 1)
Yes, mallets bought at a music store (or anyother type of store) would be considered professional instruments and are not permitted under Construction rule 3b.
(section: 4 / paragraph: c / sub-paragraph: ii / line: 2)
There is no penalty for instruments being able to play additional notes outside of the required range.