Likely you have not installed it correctly. First you must lift the lock on the hinge, then press the hinge firmly into the mounts, then snap the locks into place.
Yes I believe they are made in Wisconsin, USA
I don't know what bleach might do to it. I'm cautious about strong chemicals and they can strip the finish or penetrate and leave visible signs where it penetrated. I don't recommend using chemicals that are colored (just as an example lysol bowl cleaner which is more of a gel) as it will stain.
I think its wood. Has a very nice finish and is definitely not plastic.
First, please read my review -- you may want another brand. Next, I'd remove the old toilet seat and measure your actual toilet (bolt center to bolt center). Then head to the store and measure the actual display model. Sometimes web site folks just get the numbers wrong. If your toilet (not the old seat) is the same as the new seat you're OK. Otherwise look for another product.
White and ivory (i.e. light beige)
I've never tried it, but I believe you could. I weigh about 196 pounds and can seat on it without any problems. The seat is solid wood. I'd think the weight of the person standing on the seat would be the ciritical factor.
All round seats are the same dimensions: they must fit the industry standard of round bowls.