Not really... In Fate terms an element would be what they are attuned to and the spells are the results. In Sakura's case yeah, but Gojo's Limitless technique isn't an imaginary element technique. The Hollow Technique Purple just produces and pushes an imaginary mass which is different from an imaginary element.

he actually. tried killing Gojo. three times but failed cause he just couldn't even write up a defeat

Servants can be summoned more than once. So, yeah. No servant is confined to a certain Holy Grail War.

Really good story at this point. But once again I do want to emphasise on Servant choice. Don't follow with the poll if it's too far fetched. Give it a think on what would be a good choice and what could develop the story more. Kiara most likely wouldn't work as she's an alter ego. So kudos for not picking her. But Raikou on the other hand is a bit hard as there's the issue of trying to come up for a reason for their compatability. Otherwise the story is going good.

Anyways I'd suggest with going for a servant that has good compatability or will develop the story. Don't just go of the votes and polls. Usually will screw up the flow of the story if it's not somerthing you planned.

YES YES YES