1.) The base xp is double so is the bonus xp the same amount as well? example: 80 xp normally becomes 160 base. would the bonus be 80 or 160?
2.) Will bonus xp gaining equipment like first age, clan avatars, and alters be modified aswell? example: dragon bones which give 252 will give 504? plus the 12% from first age and avatar would be 564?
If you have bonus XP in a skill already, during DXP weekend it'll stack for 3x the XP. So, something that would normally give you 80xp will give you 240xp over DXP weekend, if you have bonus XP in that skill.
POH altars won't be included in the doubled XP, so Instead of Prayer, a skill like Herblore, Crafting, Construction, Summoning, etc. might be your best bet to save the most money possible. Clan avatars will be included, and I'm almost certain that skill outfits will be as well since they have been in the past. For bonuses like the clan avatar, the boost (3% or 6%) isn't doubled, but it would stack onto the doubled XP at the same 3%/6% rate.