I think your best bet is to install management tools on whichever box you will be running the provisioning script from. There area host of cmdlets that will help you out on this journey.
Remember in Exch2010 and later the database/server isn’t a 1:1 relationship thanks to DAGs. it’s often easier to simply target the DB directly with new-mailbox -database “blah” and move on.
You can also use the “isexcludedfromprovisioning” flag on the individual Database to block automatic placement on databases you feel are “full” or you are simply trying to avoid accounts from being made on. Finally an RBAC filter can hide different databases from different teams if you plan on having different groups managing unique server groups, for example the HelpDesk team for “wingnutz LLC” can only see/place users on the wingnutz database … no matter what server it’s hosted on.