Today I fitted a Shimano Deore 11-51T cassette, the M5100 11-speed rear derailleur and the BB-MT800 bottom bracket. All went smoothly, but I won’t know whether there are chainline problems until I fit the front chainring and the chain. Some washers were included with the bottom bracket, presumably to help adjust the chainline.
On the front I’m planning on a single chainring. The 51 tooth cassette looks huge — I’m looking forward to using my “Granny Gear” to grind my way up some steep hills!