When I set up my raised beds, I rented a cement mixer, was well worth it!
Beautiful looking bud there Dude, really nice colour Love the amendments you can buy it by bag there. come in tiny bags here about 1L
Maybe a drum, ive seen photos on line no idea how ot make one but was thinking of something like this
or something similar maybe, probably better ones out there, maybe once added up a used cement mixer could be cheaper, no idea though
https://www.growseed.co.uk/blog/how-to-build-a-diy-compost-tumbler/