Price ranges are all over the place, depending on whether two people start a bidding war on an item. I'd say: Min Bid should be high enough so you are not angry if the item is sold for that price.
I had lots of surprises about prices and bids over the years, so I won't give recommendations beyond that... ultimately, you need to make your own observations about pricing and what sells where; this hugely depends on your fan base.
Charity: Whatever you feel comfortable with. If you want an indication, just go with 10%. (There are artists who do not have any charity percentage at all, so that's possible too.)
