Can I do the Hyvä migration myself?

Yes if your team has shipped a Hyvä migration before. No if they haven’t. Specifically:

• You have a senior Magento dev who’s done at least one Hyvä migration: DIY works. You’ll spend ~70% of the calculator number in cash and 1.3-1.5x in calendar time. Best if perfectionism matters more than schedule.
• Your team is strong on Magento backend but new to Hyvä: Hyvä has an official 12-hour video training (free) and the docs are excellent. A senior dev can self-train in 1-2 weeks, then DIY. Expect 2x the calculator number in calendar time because of the learning curve mistakes.
• Your team is mid-level Magento or all-frontend with no Magento experience: Avoid DIY. Magento backend has too many sharp edges, integrating Hyvä Checkout with B2B, debugging Magewire performance, getting the cache-tag invalidation right. I’ve cleaned up 6+ “DIY Hyvä gone wrong” projects, usually ends up costing 1.5-2x what the calculator quoted.
• You want to learn: Hire me for steps 1-3 (Audit + Compute + Sprint plan), then have your team execute steps 4-5 with me on Slack as a fallback. Costs ~30% of the full engagement and your team owns the codebase.

The Hyvä community is generous on Slack, even DIY teams can usually get unstuck quickly. Not a substitute for shipped experience, but a real safety net.