Yes, most people give gifts at Bachelorette parties. Usually it's some kind of gag gift, like a sex toy or a genitalia shaped candy. Bachelorette parties are basically just a fun night out before the wedding.
Usually, yes. What you give though depends on the kind of party and the personality of the bride. It's common to give personal items like lingerie for the honeymoon. If you aren't sure, something like a gift basket with things like scented body lotions and bubble bath makes a good gift.
This is optional, but most people do not since those invited often gift at the bridal shower and then again at the wedding. Brides, however, should gift those attending, especially wedding party members.
Yes of course,if a bachelor has invited you with all his love and affection then you must take a materialistic gift which could be any thing of his taste. Or you can do is you can simply ask him if he is willing to buy anything else and is in your budget.