1. Yup. They're establishing the pecking order. It gets really wild around week three when the chest bumping starts. My girls also jumped on each others heads around week 5. It seems to have lessened since they went into the new coop. Either they're less stressed because they have more room, or the order's been established for good now. Head hen emerged very early, in week 3.
2. Probably not. Everything wants to kill a chicken, so they need to be on the skittish side. The hawk instinct is very strong; they will react to any movement coming from above. Move slowly and you will calm them. They should get used to you and bond (use treats!), but only half of mine are what I would call "friendly". One is downright needy.
3. It depends. Some breeds there are tells right away (a female BR has more black than a male BR). Sometimes you have to wait for the comb, or the wattles, or the feathers, or the stance. I got one roo in 12 pullets, and I began to suspect around week two, when he wasn't feathering in as quickly as the others. At 4 weeks, his comb popped way the heck up and now, at 6 weeks, I'm sure. Some people of this site are still unsure as late as ten weeks. After about 4-5 weeks, you can post photos here and get some expert opinions.
Good luck!