Hello there, welcome to DreamHost. We don't offer cpanel, we're proud to have our own custom-built management UI since 1997 The functionalities are similar and if you're familiar with the technology you should be able to adapt quickly to it. Let us know if you have questions, and remember to check also the documentation on https://help.dreamhost.com/hc/.
Phone support is offered as a premium support tier, details on https://help.dreamhost.com/hc/en-us/articles/215721217-Does-DreamHost-offer-phone-support-
Is the domain of the current site on DreamHost already? If not, follow these steps:
One path forward is to create a new domain on DreamHost Panel, fully hosted, like example.com. Leave the default directory, /home/youruser/example.com.
Then create a subdomain, fully hosted, called staging.example.com and assign the same folder to the subdomain, /home/youruser/example.com.
Do your development, test the site on staging.example.com and when you're ready to go live point the nameservers to DreamHost and change the URL values in WordPress dashboard from staging.example.com to example.com.
If the domain is already existing on DreamHost, then the process needs adjusting. Let me know what the case is, I can provide more details.