I think you realize this, and I might be missing something.
In order to be able to make tax-efficient withdrawals from your HSA to fund your 5 year Roth ladder seasoning period, you'd need to have qualified medical expenses to substantiate the withdrawal. In particular, those medical expenses, in order to qualify, would need to have been incurred after your first HSA funding. (*)
You sound younger, so if you're healthy, and you probably are, you might not have enough qualified medical expenses. You could still withdraw from the HSA if you wanted, but the federal tax penalties might make it not worth it / might make another option, like straight taxable, better.
(*) Technically depends on state trust law, but that's the rule in my state and is a common one.