RE: What should I expect to break
Depends on the type of helicopter I suppose. Fixed pitch helis tend to have fairly strong blades that really take a beating, you really gotta hit them hard to snap them. More commonly broken things are the tail rotors, flybar, ball links and landing skid. Landing skid is probably the #1 broken thing on fixed pitch helis, as they're often thin and flimsy. In a collective pitch bird, it can get a bit uglier due to the high head speeds. You're looking at blades, tailboom (from a tailboom strike), swashplate, main rotor spindle being bent, flybar, stripped gears, and the landing gear (on some helis, not all break so easy).
Some stuff is easily repairable (like landing gears) but some stuff, it's nice to have spares, like main blades.