I want a double up front, most of them seem to be marketed as 2x10. Are they only suitable for narrower 10 speed chains or will they work fine with a 9 speed chain and cassette?
Should be plenty of 9speed kit still out there
Other than 22/36 virtually all have been spawned by the 2x10 'revolution' though.
It'll be fine. You could just stick 2 rings of your choosing on your current cranks - TA Chinooks work well. I liked 28/40
Can I just take off the small ring on my current 22-32-44 set? Or do I need a spacer or something ? Other than setting the limits of the front mech?
So 10 speed chain rings are no different to 9 speed? Its just the chains re narrower for the more compact cassette?
You can do that, but it achieves nothing other than saving the weight of the granny ring. If you get a 'proper' double, or put smaller rings on your current cranks then you get a better chainline as you use the inner/middle ring positions.
Internal diameter of 9 and 10 speed chains are the same, so rings are the same thickness, that doesn't matter for what you're proposing though - you can use 10 speed rings on a 5 speed bike if you want. Just the other way round that can cause issues.