So this craft is almost done but crit will be tough. What I would do first is p ex you’re suffix for a chance at crit, +4-5 or surpassing. If it doesn’t hit one of those, use a dextral crystalization and p haste to roll onslaught. Do again and if not good, essence cycle with crystalizations until you have onslaught and +3. Then you have to desecrate crit chance. There’s very small chance you can hit +skills,crit, or surpassing or ias on p ex but super rare. If you do get those you may want to just p battle instead of onslaught. Or if +5 onslaught and crit desecrated.
Try it out on craftofexile first see you’re odda