khuff

Making masah on the khuff

Q:

1. If a person fulfils all the four faraiz of wudhu and puts on the khuffayn, can he offer salah?

2. Later after performing full ablution, can he wipe over that (do masah on khuffs and read salah)?

3. The farz of washing the feet,including heels. Does a person have to pass water i .e. do khilaal between fingers? Is it a farz too?