If you have any mail domains set up on your Hestia installation, and want to continue receiving mail for them, I’d strongly recommend leaving port 25 open.
Having a lot of connection attempts is just business as usual on the internet. If you’re worried about the number of connections attempts, perhaps there are other ways you can limit it. eg. if you know that legitimate senders will only come from certain IP addresses, then you can add a firewall rule. Or maybe you can add more blocklists to the exim config to get rid of some connection attempts. There are several things you can adjust in the exim config.