So, Rebel Han Gunner says:

During the Engagement Phase, at initiative 7, you may perform a Turret attack. You cannot attack from that turret again this round.

So does that mean you can attack again with a different turret, provided you have one? Does it mean you can use Han to fie a turret at Init 7, then use a missile when the equipped ships actual Init. comes up?

It doesn't use the term "bonus" attack, but i can see the argument both ways.

Correct. And still take a b9nus attack too e.g. from Cluster Missiles

Just as a point of clarification, the symbol on the rebel Han gunner upgrade is a Turret Arc symbol, not just a turret symbol.

The only reason I bring it up is that, currently, there are no ships with two turret upgrades so there is no way to make an attack with a different turret. It's a very nitpicky argument I know, but I've run into too many people who would argue that calling it a turret attack means the Han prevents any additional turret attacks that round unless there is a second turret

But since it is a turret arc symbol, it means that using Han doesn't prevent firing out of the other turret arc on a double turret arc weapon (as well as not preventing firing using any of the non turret arcs).