CSS class and id with the same name

Yes, you can use same name for both id and class because both parameters have their own significance.

No, there is nothing wrong, but it might be better to use different names to not confuse other developers. It is more (human) error prone to use different names.

Nope, perfectly acceptable.

A class is defined using a . and an ID is defined using a #. So as far as the browser is concerned, they're two totally separate items.

The only thing to be careful of is generating any confusion for yourself. It's probably best practise to keep the names different purely for code readability, but there's no harm in them being the same.