If I want to set up Sendy on EC2, do I need to use a domain that's used for nothing else? Or, could I, for example, put Sendy on EC2 while keeping my blog and sales page on the same domain at my current host?
Yes you can use your existing domain.
Create a CNAME record in your domain's DNS pointing to your EC2 instance's elastic IP address.
Comments
Yes you can use your existing domain.
Create a CNAME record in your domain's DNS pointing to your EC2 instance's elastic IP address.