I've created a CloudPage in Marketing Cloud, to collect email address and some other information. I thought I would be able to use the DE as entry DE for Journey Builder, use the email address to check if an account/contact exists for it in Sales Cloud, and if not, create a new one. But the entry DE needs to be sendable (I believe that wasn't the case before), and I can't make it sendable unless I have an email address (have that) and a Subscriber Key (do not have that).
Ideally I don't want to do the account/contact creation directly in Sales Cloud from the CloudPage, because I've tried that in the past and the performance was downright terrible sometimes. And I also don't want to create duplicate records, so while I could just use Email as SubscriberKey, I don't want to do that either.
What is a nice way to do this, that doesn't require communicating with Sales Cloud directly from the CloudPage?