Divorce advice

My wife (30f) of 11yrs just served me(31m) divorce papers. Before I sign them I’m doing research. We live in Washington state. I figured if we write up a contract that details our arrangement and take a video of me and her signing it that hopefully that’s legally binding. I just don’t want her to come back at me in the future. We agreed of me buying her which would be about 100k from our house equity that’s about 200k. And we are going 50-50 in child custody, we have 3 boys. Hopefully we can walk away amicably. Thanks in advance Reddit people.