magento 2 optimize site and check error logs

so i need to have my magento 2 site optimized , is super slow
check cron jobs and settings
check indexing ( think some need to be update on schedule) not update on save
check server settings for correct memory size ect php/htaccess) reduce load on server
check caching settings ( possibly install Varnish or recommend )
check sessions settings
check var logs
check database ( believe i have a bad table) maybe permissions have seen issue during compile
check store mode ( developer/production/default)
check robots.txt ( add robots txt)
check sitemap.