The weighted pull-up and 400m are kind of more Crossfit than strongman. I'd replace the pull-up with a deadlift or something, maybe an 18'' for reps since then you can really load up the weight (like 300# for the women). The 400m I'd drop entirely.
What kind of stone are you planning on tossing?
Also those farmer's walks are seriously light. At my last contest the women were doing 110#/hand with handles and we were flying (I actually tripped because I was taking such huge steps I hit the plate in front of me!).
You'll probably find using three people to push a Humvee will make it too light as well. A strongwoman contest at my gym last year had each woman pull a jeep 90' for time from a seated position. A 50-year-old lady was able to do it. Maybe have two people push? Or one person at a time, taking turns?
My recommendation is you test out these events before putting them in the contest.