If you use a grand soul gem to create a weapon,will it have a larger pool of magic and soul gems needed to fill it?Or is it the actual enchantment?

A grand souls gem has a higher strength enchantment and more uses than something enchanted with a petty soul gem.

Thank you.

The size of the soul is what's important for recharging, not the gem.
Although the larger the gem, the larger soul it can hold.... Just keep in mind that large gems can also hold small souls.