Can't wait to see your new clubman build!
Either can I!

I got into this one too far, still waiting for parts to come back from being painted and I still need the wheel set and Brooks Swallow ....but time and $ cures all our bicycle ills. This one will be a very simular bike to the Pashley in construction and style and unfortunatley price, so I'm not convinced the building a vintage is less expensive....It can be but it also depends on what you want to do.
Can you recommend a suitable clubman style drop bar replacement?
Maes bend bars were the most common I think and still plentyfull at swaps or ebay
What do you mean by the quadrant shifter being a pain to shift?
It doesn't have detents or stops so you have to fish around for the hole for the post to catch on, it soes have little ramps but they don't always catch the hole. Once you get used to it, it's reasonabley fast but you still have to take your hand off the bar to shift. The barend or trigger has detents and you don't have to move off the bar to shift .