ワロス is a famous and popular internet slang that means 笑える or 笑う. ワロス sounds like a false archaic Japanese, and is thus funny to us. But we don't have such an archaic Japanese word lol.
Your ワロタ is ワロス+jodōshi た

ワロタ, the past tense, and this would sound 笑った in many cases.
According to
this page,
『枠取り作業お疲れ様』→枠取りお疲れ様→枠乙→わくおつ→わこつ
I don't know well, but in ニコニコ生放送 a user needs to get a broadcasting? frame (枠).
Wakutori sagyō otsukare sama has become わこつ. But now users can get a broadcasting frame much easier than before, so わこつ seems to mean "I've come up now."