Hey Jurgen,
Jurgen Verhelst wrote
Some headscratchers;
1. Transfering should be quick, I should be able to change the header from the old site to the new one within plesk, but how will DNN react to that, I assume much is linked to dev.domain.com and just changing the header wont fix that.
In addition to changing the header, you'll want to create a new portal alias for your portal. You can do this from the Host->Portals page (near the bottom once you "edit" your portal - you'll see the header "Portal Aliases" and can "add new alias" from there).
Portal Aliases are used by DNN to map the incoming URL to a particular portal - this way DNN knows which one to use. Without creating a new portal alias, after updating the header in Plesk, when you access the new URL, it will redirect to the old portal alias.
2. Could I take a backup of the DNN site on dev., create a empty DB on the www. hosting and quickly delete the contents there and restore the backup to it?
You can certainly take a backup of the database and restore it elsewhere. DNN is an asp.net application like any other and allows for (relatively) easy movement. Make sure you backup the complete filesystem (the entire root of your website) and also the complete database. There are settings in your web.config that must match that of your database, so you can't go mis-matching the filesystem and database.
3. I've learned DNN can hold many portals, so you could host many sites on one installation. How commonly is this used in 'the field'. I could imagine that when a user on portal 201 writes some crappy code, all sites on that DNN could crash?
This happens in the field quite frequently, but really that's irrelevant, because it's all about what is right for your particular needs. If they are "small" sites that are not mission-critical then having multiple portals within a site may be fine. But if it is in any way mission critical, I'd suggest splitting them out. Of course this means managing them will be that much more complex. Bottom line is that it is more simple to share portals, but not nearly as configurable (or complex).
Hope that helps,
Ian