Can I do the upgrade myself?

If your store has < 5 extensions, no custom modules, and you’re comfortable with composer + bin/magento, yes. Adobe’s own upgrade tool handles most of it. The cases where DIY usually goes wrong: extension conflicts, broken indexers post-upgrade, payment/checkout regressions you don’t catch in QA, missing data patches, and the dreaded composer.lock conflict between core modules and theme overrides. If your monthly orders have a comma in them, get help.