Bleeds: There's generally no such thing as "too much bleed". With that in mind you can generally use what you feel comfortable with as long as it provides a minimum for trim errors. So a minimum would be around 0.0625"/3pts/1.5mm, but realistically I'd use closer to 18pts/1p6/0.125"/3mm. If you go a bit over that, it's never an issue. That being posted some reproduction methods call for much, much larger bleeds sometimes easily surpassing .5"/12mm or even 1" 25mm.
Spine widths: Widths of spines depend entirely upon the stock to be printed and it's weight combined with the number of pages in the book.
The formula to calculate spine width is essentially --
width of 1 sheet of stock x # of pages = Spine width Therefore it is pretty impossible to know a spine width without first knowing what stock will be printed. Once a stock is selected, most print providers can supply the width of the stock, if not the width of the spine directly.
Hard Rule: Anything which extends to the edge of the page and is to be printed must have a bleed. Even if that means it's a color-filled text area. If there's color at the edge, it must bleed.
If you are ever unsure about set up for a print projects, it's always wise to consult the printer. Typically, they'd much rather have a 10 minute conversation with you than spend days going back and forth rejecting print files due to improper set ups.