This is an oversimplification, but . . .
1. Yes, you can use new attributes.
2. No, you can simply toss all of them out the window and make your own.
2.a. Basically, you have to make all the mechanics Open Content.
2.b. You can declare the names closed or IP.
2.c. You can change the race.
3. You can make your own experience system and/or progression system.
4. You can make your own HP/damage system.
5. You can just cut and paste the
SRD.
6. Basically, rules/mechanics that affect anything from the
SRD have to be open, as does anything taken directly from the
SRD or other open content; everything else can be closed.