「あの[洲]{す}よか、こっちっ[側]{かわ}[中心]{ちゅうしん}に[攻]{せ}めるってことでねー」
- How the second line translates? Literal translation is preferred as I'd like to understand every bit of this line.
"So, we/I should concentrate our/my attacks on this side of that sandbank, eh?"
「よか」 is a more informal form of 「よりか」, which is already informal. The more formal forms are 「より」 and 「よりも」.
「あの洲よかこっちっ側」 means "this side, rather than the other side, of the bank". In other words, "the speaker's side", "the side that is closer to the speaker", etc.
- What's the reading of 側 here?
It is 「かわ」 unlike what was said and even upvoted in the comment above.
If it were 「こっち側」, then the 「側」 would be read 「がわ」.
- What second っ in こっちっ does here? Is it an accent/colloquialism, or does it stand for something?
The small っ makes it even more colloquial/informal. This can be said about so many other words as well.
In the order of formality: こちら側 ⇒ こっち側 ⇒ こっちっ側
Other examples:
「[人懐]{ひとなつ}こい」(amiable, sociable, etc.) ⇒ 「人懐っこい」
「めちゃ」(very) ⇒ 「めっちゃ」