Hi Folks
I think after some further investigation I think I've got 2 issues. The hot-starts are smoother since the swapping out of the plugs but I'm still getting some odd noise and clattering on start-up. I also noticed a similar noise can occur momentarily on blipping the throttle.
I grabbed a camera and filmed the aux belt area with the engine running (look further on for slow-motion footage)
As you can see for a fraction of a second there's allot of belt chatter. Given the hot-starts can be irregular as well I think that's causing extra noise from the belt area. It's generally quiet at idle so I'm assuming it's either the tensioner or possible a very early sign of the alternator clutch pulley as I understand that is designed to smooth out/deal with engine vibrations.
Depending on how long I keep the car (I'm currently running it as a stop-gap) I may swap both the pulley & tensioner.
Will keep everyone updated.
Thanks