Yes, another vote for a short-travel FS 29er please.
430mm chainstays and reach of 460mm on the medium. I’ll leave the HA up to you. 125mm travel would be my choice, but I’m flexible if that impacts CS length
There will be a weight difference due to the 145 handling a 160mm fork – but the bigger difference is geometry, with the 145 being 2 degrees slacker with a 160mm fork, and the feel of the extra travel.
I think you mean the brace that’s joining the seatstays? Stiffer than just having separate stays meeting either side of the link that drives the shock.