Thanks for the responses, guys.
I had considered selling the finder and going for an all-in-one kit. Some are very reasonably-priced. Unfortunately, there are various issues in attaching most of the cheaper kits to the top side dovetail bar of the OTA which, for the sake of brevity, I won't bother going into.
I decided to buy some throw-away used eyepieces and just unscrewing the barrels. This actually turns out to be rather cost-effective if a little wasteful.
As for the finder attachments, I still can't find any details on the thread gauge of the tube, so am taking the vendor's words on trust that the attachments fit the onto the finder tube.
I gave ModernAstronomy a go (which was very helpful - thanks for the pointer, there) and found these:
http://www.modernastronomy.com/shop/accessories/adapters/sky-watcher-clones-to-t-thread-adapter-for-straight-through-finders/
http://www.modernastronomy.com/shop/accessories/focusers/t-thread-to-1-25-helical-fine-focuser/
The helical eyepiece focuser is needed to bring the sensor to focus. There are non-rotating alternatives for roughly the same price but not with a female T-thread on the scope side, adding the need for more adapters and thus extra cost.
I'll post updates once it's fully assembled.
Thanks again
Lewis