How to route multiple web apps on several AWS EC2s under 1 domain without using a bunch of Elastic IPs?

Last night I realized that there is a 5 address limit with regard to provisioning elastic IP's.

Ive done some initial research, and have come to the conclusion that a bunch of elastic Ip's is probably not the correct answer. I feel confident that I can add startup scripts to update Route 53 dns records at startup to circumvent the need for static ip addresses, but from reading, it seams like this could lead to issues with down time from DNS caching. For things like the phone system, website, and mail server; this would be less than ideal.

In your experience, what is the "Right" way to handle a situation like this?

For reference, I'm developing the infrastructure for my new small business, and thus far I have the following EC2's:

1. PBX phone software by the company 3CX. This ec2 is not using an elastic IP. The company 3CX provides me a 3cx domain to use with my desktop/mobile software.
2. Samba Server to provide network file sharing. (Elastic IP)
3. Online accounting software (Elastic IP as a subdomain by Route 53)
4. Wordpress sever main website (Elastic IP as a subdomain by Route 53)
5. Softether VPN to provide access to the Samba Server (Elastic IP)
6. MailCow Mail Server (Elastic IP as a subdomain by Route 53)

Many thanks in advance! :)

I have a few suggestions:

• I would use managed services where they're available, rather than doing things yourself. AWS VPN service, a hosted email server, online accounting software (I use Xero), hosted PABX, hosted Wordpress (e.g. WPEngine) would probably be a LOT easier than hosting your own. It might cost a little more though.
• Instead of a Samba server why not use AWS EFS? You have to use DirectConnect (expensive) or AWS VPN (fairly cheap) to access it from outside AWS.
• If you run out of Elastic IPs you simply request more from AWS. It's a soft limit. Google "AWS elastic IP limit increase" but the steps are

Steps

• Open the AWS Support dashboard.
• Choose Service Limit Increase.
• Important: EC2 service quotas affect one Region at a time. You must request service quota increases in each AWS Region where you need more resources.

You might get more useful answers if you ask a more open ended question about how to achieve your goals, rather than asking how to do things the way you've thought of.