Glad to know you have migrated Blogger site to self-hosted WordPress site.
Error establishing database error occurs due to wrong database credentials. I guess you have fixed it as the site is loading fine now.
Blogger.com and WordPress permalinks structure are different. If you are using same Blogger (custom domain) for WordPress site then changing permalinks structure will help you to keep same links as Blogger site.
You can refer this tutorial https://rtcamp.com/blogger-to-wordpress/tutorials/permalink-seo-migration/ to do configuration and settings to avoid site traffic loss.