My qusstions:
1) What should I expect out of clipless on my mountain bike?
I have no Idea about what you expect, you tell \Us /me..
2) What advantages do clipless pedals have over platforms?
You have to buy both the pedals and the shoes
You have to buy both the pedals and the shoes that are compatible
3) What advantages do platforms have over clipless?
you can wear any shoe you wish
you wont have your feet attached to the pedals like a ski Binding. maybe you want big air when you come over a jump?
4) Which shoes and cleats do I want?
How should I know , go to a Bike Shop and try on shoes to see if they fit, and ask the staff in the store about the various products
the cleat comes with the pedal system .
SiDi Makes the Best Mountain Bike Shoes .. In Italy .. they have a lot of width and sizes
metric whole and half sizes in the middling range where most peoples feet are .. 40 to 50..
and use a synthtic leather , so soaking your feet doesn't ruin the shoe , like Natural Leather has been shown to do .
... where many Chinese made shoes wont fit, the best. though may cost less .. and may be OK as starters ..