The Shoeless Joe Professional Series Baseball Glove: 1150HW will probably be a bit big as for the hand opening of the glove. The Shoeless Joe Professional Series Baseball Glove: 1150HW will be the right size in the 11.5'', but might need a model to squeeze his hand adequately.
The Shoeless Joe Professional Series: 1150HW is an 11.50 inch model. This is a great option to consider for a 3B. To answer your other questions, (1) this glove is not in our showroom currently so not sure on the weight (2) the 1150IW is another good option to consider (3) difference between the web design is purely cosmetic and has no affect on the glove itself; rather it comes down to personal preference as to what a player believes to be a better looking design.
This Shoeless Joe Professional Series (1150HW) is designed to fit more of an adult male hand. You could get it for a 9 year old if you are okay having an extended period of time where he will have to grow into the fitting of the mitt (probably till he is 12 years old). However, we do feature a 100 day guarantee on all our gloves and if you got the glove and decided it was not the glove for you within 100 days from the purchase, you could send it back for a full refund or exchange. In regard to your 2nd question, the pocket depth on this mitt would be fine for use in the outfield or infield if it was being used by a 9 year old. The biggest issue would be if the mitt will fit your player effectively.