I have this game but I haven't bought AC3 yet (hoping on a steam sale), does it matter which one I play first, the wiki here makes it sound like a bunch of stuff unlocks in this game based on AC3; does this game have an effect on AC3 at all?

I just finished Revelations last night and I'm planning on pushing through everything AC before the end of the year.

It might be best to play this one first, if you already have it of course. The reaction time you have while you decide to counter, throw, etc. is extremely tight compared to Assassin's Creed III's, in which you pretty much get a larger window to attack. It made combat in III go more smoothly for me, not that helps you any.

Unless you have the PS3 version of Assassin's Creed III, Liberation would have added an extra mission or two to it. Otherwise, not really. There is very little crossover between the two games in Liberation.