Caching within comment Loop

Hello.
I have additional 4 queries within the Comment Loop.
One of them counts Comments Number for the $comment->user_id. For example.

All 4 queries work as intended.
I break my Posts into comment-pages after 50 comments.
So those 4 queries cause a lot of queries on one page.

I am now experimenting with caching the query output.
I have read in the CODEX about caching, but when I apply the instructions for caching within my Comments Loop, the first ‘cache_key’-query returns ARRAY and then the page just breaks.

I also experimented with the Plugin ‘Plugin Output Cache’.
But it just echos the query in Post display.
It doesn’t interpret the query, but prints the syntax of the query.

I am seeking for help as I’ve already put some time into the issue and it is obvious that I am stuck.
Can someone point me to a guide on the Internet, or if he’s so kind explains me how I cache simple Select statements with just maximum 1 join and 1 sum operation.

Thank you in advance.

P.S: I am also using W3 Total Cache. What a great Plugin.