Custom domains for a multi-tenant SaaS — CloudFront SaaS Manager vs Caddy vs managed service?

Looking for input from people who've actually shipped custom domains for a multi-tenant SaaS, because I want to avoid picking the wrong path and regretting it later.

Current setup:

• Multi-tenant events platform on AWS
• Frontend is a React app — dist folder on S3, served through CloudFront
• Today every tenant gets a platform subdomain (tenant.stage.example.com) via a wildcard cert on CloudFront. Frontend reads the hostname, asks the backend "which event is this?", renders accordingly.
• API calls go to a fixed, separate domain (api.example.com) — so the custom domain is only needed for serving the static frontend, not the API.

What we want:
Clients want to bring their own domains (portal.clientbrand.com) instead of our subdomain. So I need per-domain TLS that issues + renews automatically, with no manual step per client.

Options I'm weighing:

1. CloudFront manual + automation — add each domain as an alternate domain name + ACM cert via a script. Works, but there's the ~100 CNAMEs-per-distribution wall, and one cert per distribution feels fragile at scale.
2. CloudFront SaaS Manager (the multi-tenant distribution thing from 2025) — looks purpose-built for this, up to ~2000 domains, per-tenant ACM. Since we're already on CloudFront this seems like the least-effort path, but I haven't found many real-world reports.
3. Caddy on-demand TLS — reverse proxy that issues certs on first handshake. Unlimited scale, but it's a new component to run/monitor, and I'd need the ask endpoint to avoid getting our Let's Encrypt limits burned by random hostnames.
4. Managed service (Approximated / similar) — lowest effort, but monthly cost + another third party in the traffic path.

Questions:

• For anyone running CloudFront SaaS Manager in production — is it solid? Any gotchas with cert provisioning, DNS validation, or pricing at scale?
• Given our API is already on a fixed domain (custom domain = static content only), is a reverse proxy like Caddy overkill for us?
• Anyone regret going the manual-CloudFront-automation route and wish they'd started with something else?

Expected scale is realistically low-hundreds of custom domains over time, not thousands. Trying to pick something that won't need re-architecting in a year.

Thanks in advance 🙏