naugmeister all of our plans include unlimited domains, apps, sites, etc. The only limits are your total storage, RAM usage, and monthly data transfer. All specs and pricing at at: https://opalstack.com/pricing.html
If disk space is your biggest concern then go to https://my.webfaction.com/disk_usage to see your total usage, then choose the plan that you'll fit into.
If RAM is your concern then run this command as your WebFaction shell user: for pid in $( pgrep -u $USER ); do grep -w -i pss /proc/$pid/smaps; done | awk '{Total+=$2} END {print Total/1000" MB"}'
That will give you your total RAM usage in MB at WF, so you can then choose the plan that's the best fit for your needs.