I've travelled on the A350 quite a few times to AUS and back. I now avoid 1K with a passion for various reasons, but the primary two are that there's a crew storage unit in front of the seat which the crew will insist on slamming shut through the flight (even if you're sleeping) and that the galley is literally right in front of 1K. You get a lot of crew traffic walking back/forth and it can get very distracting.

The toilet in that area is normally put 'out of action' by crew, meaning you have to go to the rear (behind 11K) and it feels a little darker than, say, 9K or 10K which have two windows.

When you disembark, you are also one of the last to get off from J as the exit is normally from behind 11A.

I now try and book 10K or 16K. The only downside of 16K is when you board you have to wait for a tonne of WTP and WT passengers standing in the aisle waiting to get to their seat.

1K on the A350 is nothing like 1K in F!

As for the way back, the small cabin would be my choice - 16E/F. Or I'd maybe go with 9 or 10 E/F.