Is anyone looking into starting on Substack? What's your strategy?

I wouldn't recommend Substack (newsletter operator here). They're trying to become the "everything" platform for some creators and there are point solutions that are much more effective, their strategy of going broad has backfired. Twitter also penalizes outbound links to Substack because Substack tried to compete with Twitter on several of its features back in April/May. You'll have much better luck using Convertkit/Beehiiv if you're trying to create a funnel involving a newsletter.

Planning to use Substack as a funnel for my SaaS tool. Gonna hit 'em with value first, then slide in the upsell.

Depends on what you are trying to get out of Substack!