Actually i believe they do stack, i mean when i use both buffs they do appear at the top.
And i believe that skills should be
Body Upgrade - 10% Enemy Damage Ignored 12 mins
Power Surge - 30% Strength increase 20 mins.
(Or did i get it wrong? hmmm)
Both are pretty important to me (I mean any buffs are cool) so i pretty much max both out and use them (i think they do stack, im very sure im getting more strength). And the HP Passive works wonders as well.
If your looking for a build you can try -
OGPlanet Forums: Meister Builds
or just look through the forums.