So, noob question. But is it possible to wear more than one 3D item at once, and if so, how?

as long as they are not made for the same bodypart yes it is possible.
if not the same bodypart its no
unless you find a glitch or smthing

Oh okay. So as long as the items don't overlap, it should be fine?

I should more say as long as they aren't on the same body part. So hat and blindfold don't work, but would kick n kicks and a hat work?

yes it will work.
you can wear 1 item per bodypart and 1 item per joint.
example:
barbed wire + little latching elf + both kickin kicks + swagstatic gear + both elbow pads + mecha arms...ect

you already got it anyway

It's possible to stack few items on the same part if you put all items in a set and then activate it. not sure if it's against the rules to do that though..

I thought that set glitch only worked with hairs. Gotta try some stuff out now...

It only works with hair items