lol I can't believe I'm excited for someone to watch BBUK, I never normally would be, probs cause you always said you wouldn't
I've not seen the early series so I can't comment on those but my personal recommendation would be that you at least start with one from the ~golden era~, so 5, 6 or 7. Pretty much the entire fandom considers BBUK to be at its peak (production/quality wise) through those years so! You should definitely watch a C4 series before anymore C5 ones, that's for sure