You can’t possibly reliably send mail from a dynamic address (you’ll have to use a relay service). It probably will impact your search engine ranking, but we’re not SEO experts.
We generally recommend you only use dynamic IPs for dev sites, and get something more permanent for production use.
I use Cloudflare for all my DNS, so typically the address stays the same even when my ISP external address changes.
The only time my IP address ever changes is when I have to reboot the modem, and even then it rarely changes. So I decided that it would be easier to just use the Cloudflare DNS so the address that Google sees never changes and any time I had to reboot the modem I would check the external IP to see if it changed and update Cloudflare immediately.
At most, the sites would be down about two minutes, but the cached sites would remain accessible, so nobody ever really noticed, least of all Google.