If you need helpful metrics, from someone who does collaborations (a lot) to grow an email list, here's some surface level data I found:

Bundles -> 200+ subscribers at least

Swaps -> 25+ at least

That's looking at some collaborations data I've found.

You can layer them on eventually by doing:

One bundle a month

One swap a week.

Swaps alone have helped me secure a 120k audience reach without social media...long story short you're making a great move Scott!