Question about Double XP weekend

do you get double XP for combat XP such as hitpoints and str?

And will I get double the XP per lobster that I fish?

 

it goes by a staircase of tapering xp multiplication values.

So at first you'll get 10.8 xp per 10dmg you do. (2.7x the 4 you usually get)
then after 30 mins it will step down to 10.2 xp per 10dmg. (2.55x)

A full list of the xp multiplier stairs can be found here:
http://services.runescape.com/m=news/bonus-xp-weekend---3rd-to-6th-september?allcat=true

and to the part about the lobs.. yes you'll get bonus xp per lob you fish. The amount will depend on the timing as stated above

 

Yes, and yes.

Not exactly, double, but multiplied by your base xp modifier.

 

I think it would be better if after the first day the multiplier resets.