when on holiday from work are you still accruing holiday hours?

yes, you should be paid 2x or above

Depends, if you are union or have a contract that spells it out then yes, That is one reason they don't like to let people schedule vacation around holidays. When I was a union employee in a 7 day a week job if the holiday fell on my day off I still got 1.5 time, it I worked that day I got time plus 1.5 time. If I took vacation over the holiday I only got 1.5 time.

On holiday, usually yes. On a leave of absence, usually no.