I plan on giving Ice Ball to my Swampert to handle it's grass weakness as well as yawn, but I want it to be more powerful so will giving it a Metronome make Ice Ball more powerful?
No,it will not. According to this http://pokemondb.net/pokebase/98592/questions-about-the-metronome-item,metronome metronome only boosts rollout everytime you select the move.The same goes for Ice ball. Only these moves will be boosted by Metronome:
http://bulbapedia.bulbagarden.net/wiki/Multi-strike_move
Hope I helped!
Yes it will if you use the same consecutively
When this item is held by a Pokémon, if the holder uses a move multiple times consecutively, its power is boosted by 10% of its original power. The effect stops increasing after the 10th turn and resets if another move is used.
Source
Hope this helped!!