One IP address is all that is really required to host any number of websites on a single VPS (subject to your Plesk License).

However, you will need two IP addresses if you intend to run your own custom DNS services on the VPS, unless you make use of a Secondary DNS service.

You will also normally require a dedicated IP address for each site that requires its own dedicated SSL certificate.

Additional IP addresses are available at a cost of £2.50 + VAT per IP per month (All additional IPs must be justified)

Please see the Additional Details and FAQs page for more information