Good questions.
To answer the burn-out point: I think this is something writers have to take into account when they're starting their publishing businesses. Running a publication is definitely a demanding exercise and it is often under-estimated. That said, I think Ben Thompson, for example, handles this problem well: he makes it clear to Stratechery's subscribers that he regularly takes some time off to recharge, and he lets them know well in advance when he's going to take a break.
This is one of the areas we hope Substack can be helpful in, actually. We are building up a knowledge base of best practices, informed by the people who are publishing with our tools, so we can help all kinds of writers succeed. Part of the advice we offer relates to content strategy, pricing, cadence, etc, and part of it relates to less tangible stuff, like how to manage your own time and expectations.
And yes, converting readers from free to paid is a huge and unending challenge! We focus a lot of our effort on solving this very problem. One small piece of advice we offer is for a writer who is contemplating going paid to clearly signal the transition in advance to their readers, then give them incentives to subscribe early – like a special charter price, for instance. More broadly, Neil Cybart from Above Avalon shared some useful thoughts on the subscriber model recently. This comment stood out:
"Going from a scenario in which all content was public to one in which only a fraction of content is public can be jarring. Most sites have handled this transition by keeping content free and instead giving paid subscribers a very marginal amount of exclusive content. In essence, sites are treating subscriptions and memberships like donations. This is not sustainable for or attractive to subscription-based models."
What Neil is saying there is that it is better to set the expectation that the bulk of your content be available only for paying subscribers.