I agree with Nanren. (Note that the first sentence of his answer is meant as a joke.) The sentence with the word “first” is grammatically correct, and the meaning is not inappropriate, but that’s not how we speak English. You’re just translating 先 from the Chinese 我先走了 (or 吧? I get confused with those final particles)。Don’t translate 先; it doesn’t have an English equivalent in this context.

I'll answer first as Aaron's decided to only comment. :) . He's right :) . See you later, guys. Later, guys. Must go. Must go. Have ..<something>.. to do. It's time I should be going. .... Gee, is it that late, already. ..... Have to abandon you, now. See you later guys. Gotta go. ...

The word first is fine but since you haven't left yet you would say "I will be the first to leave," or "I'll leave first." However, in casual conversation with your friends there is no need to call out who is leaving first. In a conversation, I might just say "see you guys later." Or give a reason why you're leaving like "I'm tired. We will see you guys later." Or "I have to work in the morning, See ya"