In theory, its not possible to use a Shimano 12s cassette because the cog spacing isn't the same. It only work because the difference is very small.

For increasing the chainring size, the limitation is the chain tensionner around the chainring that hold the chain while the Birdy is folded. I think the maximum chainring size is about 56t.


For the hubs with XD and XDR freewheel (for 11s, XDR is not needed, XD is OK) is 135mm with quick release, I know the Hope RAS4 and Tune Climbhill. The Hope is cheaper than the Tune and a little heavier (but weight much less than the Sunrace). But there are also from some other brands Bitex, Extralight, Hubsmith, look on the Ginkgo (my wheels were made by Ginkgo, they are specialized in special wheels, small diameter, wheels for trike and velomobile...)
The fact that they aren't on big webshop in 135mm QR5 is due to because the demand for this spacing is low, most new bikes have 142mm/12mm several of these hubs have exchangeable axle and are convertible is several spacing and axle diameter, my Tune hub was delivered wrong type by Tune = 142/12mm thru axle and Tune send me a conversion kit to 135mm QR5, the conversion can be done without any tool. Same for the freewheel body, its convertible. For instance the Hubsmith wheelset of the Pacific Cycle Birdy R20 11SP can be converted to XD/XDR.

If I was you Cebep, I would use the Birdy with its original Sunrace cassette and see what happen as I did with mine during about one year. Besides the issue of Glye, the transmission works very well with smooth gear changing, the gear inch range is excellent, the only complain I have is that I have the impression that the cassette wear faster than a more high-end cassette.

For the Shimano Ice Freeza discs, they wear faster than the steel discs and make much more noise when braking hard, I do not like them much, I switched to it only because I needed a centerlock disc and didn't want to use a conversion 6 holes to centerlock.