Should I roll out to everyone at once or in stages?

Stages. Always stages. Start with two or three people who are open to trying it, let them run for a couple of weeks, learn from what works and what doesn't, then expand. Every team that's tried the big-bang approach has regretted it. Staged rollout gives you time to tune the guardrails, build internal expertise, and create advocates who help bring the rest of the team along.