This may well be a silly question, but are the roadie 11 speed components all interchangeable? For instance using 105 chain rings on an Ultegra chainset or a Dura Ace rear mech on 105 shifters? I suspect it’s all fine for mix and matching but wouldn’t mind some reassurance before I splurge out the wallet.

Yep, go nuts.

Yup, apart from the usual stuff like:

Ultegra and DA brakes only have clerance for 25mm tyres (officialy).
105 has an option of a 5 arm chainset which obviously wont work with 4 arm rings.
Tripple and double shifters and front mechs.
Rear mech capacity (both in terms of max sprocket size and whether they can cope with a double/tripple).

Thanks all.