Alright so I've got no experience at all with customizing guitars. And basically, the pickups in my SG are dead so I gotta get some new ones, and I wanna try something interesting with it. Currently has two closed top humbuckers in it.

How easy would it be to put a couple of single coils in there for a start? Can I put two in one humbucker slot and wire them up together? Or does that defeat the object of having single coils? How easy it to install pickups full stop?

And suggest some other combinations of pickups for us? I wanna try something different but not too over the top.

It's possible but you would have to reroute it a bit and it may end up looking quite home-made. But if you don't mind refinishing the guitar then the possibiliteis are endless, you could fill in the gaps with scrap wood and paint over it, it could look quite proffessional.