Can't access premium content on new domain/site


We have a new domain name and web host. I am in the process of setting it up to import all the data from our old site (the one I am on right now). I started to install all the plugins on the new site, and plan to also add the theme and make all necessary mods to it, etc, and set everything up BEFORE I import our backup. I have already made all the URL changes to the backup file (over 6,000 places where the URL had to be changed).

Problem is, I can't install the premium content (plugins). I can't install WPMU DEV Dashboard . I have my API key from this install, but have NO place to put it so I can get the premium content.

Once everything is imported into the new site and tested, we will cancel our old hosting service. The 'old' site will 'go away'. BUT, until the new site is working perfectly, I will not get rid of the old site.

Please advise me how I can get the premium content, install WPMU Dev Dashboard, and have our API key in it. We are supposed to be able to get up to 20 WP sites with the level of membership we bought.

Thank you TONS in advance!

Mary :o)