It would be totaly same on cloud environment, only thing where you need to put your effort is domain controller for setting up the LDAP otherwise rest is same. and yes need to open few ports between CMS , DB and CD servers.
Usually your architecture vary only for the DTAP environments not wheather you are using cloud or your local servers.
Dev Environment - can have separate servers for CM, CD and DB each,
Test Environment - Separate one server each for CM, CD and DB;
Acceptance & Production - Should be in sync for configuration point of view. Cluster of multiple servers for each CM, CD and DB
Answer for your questions:
For licence you need to follow same procedure, need to provide the servers name and cpu counts.
No addition space is required.
This depends on your DTAP environment and hits on your site.
No impact would be in case if upgrade database on cloud.
In content delevery server you only install server roles, if you only copy serever roles from your existing server to cloud and do update the licence files, configuration files then it would work.
As far as I know things like Amazon RDS and Azure Databases - any Database-as-a-service - isn't supported ... yet. So you'll need to use a virtual machine with one of the Tridion-supported databases on it.
But apart from that, if you provision adequate virtual machines running the correct OS prerequisites for Tridion, the installation is no different to physical kit.
There are probably a few gotchas specific each cloud provider - security, firewalls etc, but the installation process for Tridion should be the same.