Since you get SO slots, I'd wait and order chèvre. Chèvre and Togo are my favorite carefree leathers for sellier, and it looks like Togo's no longer available

Box and Sombrero are not carefree. Barenia is, IF IF IF you like the saddle leather look. I LOVE Barenia but, to me, it's not ideal for a sellier 25. I owned one and it was absolutely stunning; I regret letting it go; but I do believe Barenia is best in the kind of bag you throw around. If you do not mind a sellier K getting marks, scratches, patina - then I'd try for Barenia. It will last forever and can even be in rain and snow. (You are very unlikely to see anything but Fauve color, though....)
ALL that said, although everyone knows Epsom is a dealbreaker for me (none of my stores even bother to offer), I had a situation recently where I was looking at a bag and there was a K32 noir Epsom. The woman who was offered it asked my opinion (masked and distanced of course). It WAS really beautiful. I've had this same experience before with noir Epsom bags - I might not take it but I don't think anything is wrong with it. A black Kelly is such a classic, and if you like PHW....25 with PHW would be such a cool bag.
TL;DR: If you can SO chèvre, do that; if not, this is a VERY coveted bag as you know
. If you are a PHW person (and again assuming you can't SO chevre) I'd probably snap it up.