yes, you can make custom skuls in at the very least firefight mode.
There are no skulls in Halo Reach.
You click on the tab that says skulls and you click on the skull.
No. You are given them all.
No, only Oddball.
practice practice practice :)
You can, just like in Halo 3. It will have more skulls in it too. I'm not 100% sure what all of the names are and their functions, But I will test it VERY soon.
In the wave options when customizing a firefight game.
I don't believe you collect any. You just turn them on or off.
Nope
So far, the datapads in Halo: Reach have no function, but it is possible that, as they did with the skulls, Bungie will add some type of reward or mini-game for them to follow.
Search for Halo 2 skulls on www.youtube.com and there will be a selection of videos showing the wereabouts of the skulls or how to get them : )
well depending on what skulls you turn on the skulls will make it harder [usually] or more fun [only two actually make it fun] but will improve your skills and give you more points