I have someone interested elsewhere.
However they want it for a drop bar gravel bike which currently has a 1x set up.
What brifters and other bits will they need to buy to use this 105 stuff?
Depends what's on the bike at the moment, and what type of brakes it has. But they'll want front and rear shifters (the most expensive part of the whole groupset) both mechs, cassette probably (but not necessarily) the chainset & BB.
I changed my (drop bar, mechanical brakes) bike over to 105 R7000 a few years ago. TBH if I was in that position now, I wouldn't really be interested in your offer because all I'd have been getting that would be useful to me would be the mechs (which aren't too expensive anyway) and the cassette. I'd still have had to source the shifters, crankset and BB.
Just the chainrings, and not the whole chainset would have been no use to me back then because I had a (completely worn out) SRAM chainset that I was removing so I wanted the whole thing. And your putative buyer is going from 1x so probably won't have a suitable crankset (unless they have one in a box somewhere)
Hope that makes some kind of sense.