I'm reading between the lines here, but my guess is that you're interested in the coffee role because you're passionate about coffee. It also sounds like you've looked at the pay cut, and decided you can live with it. (Take the long view ... if you make a career of this job, will you be able to afford to live where you want to? Will you be able to comfortably retire?

I suspect that if after a year or two you decide that this more manual work isn't the life improver you expect, you should still be able to get another job in your current field. It might be a little harder than if you were to look for a new job without the gap, but will be much easier than breaking into it in the first place.

You can also talk to your manager -- they might be able to offer you an unpaid leave of absence for a while which would give you the space to try the new job while keeping your options open.

I'm familiar with the finance industry in NY which has a heavy work-hard-play-hard culture; or put another way, they have demanding expectations, but pay you enough for you to tolerate it. I assume London is similar. Switching to a similar sales role in a different industry might be an alternative that could work for you as well. It might be less of a pay cut, but give you more capacity to pursue things you're passionate outside of work.