Depends on software level, any slot except would do but slot 11 was used as option card only slot in versions 2 and lower. but to be safe don't put it in slot 11.

Master clock is for time sync from exchance, it would be the pri but if you have basic rate isdn it could be the bri card.
I still think you should get help from a tech, this should take about 30 min to setup by a trained tech.

“I have not failed. I've just found 10,000 ways that won't work.”