I have used FREE time on Azure, Google Cloud & AWS...so, yes - it's possible!
But have to check it out, if it's a Win setup...Linux is more stable...
;)

Yes after the free trial they ask you to pay. Most of them just stop the VM if you don't have credit. I just stopped crunching when my credit was gone. I'm wondering of using this type of service for on demand GPUs instead of buying a system. But this is not important for this project. You still have to pay if you don't use it, that is why I didn't pay money for a service yet.
You can upgrade your VM with more CPU for example. Depending on the system it is easy or not. You have to just configure it an restart.

I tested the following services:
* Google Cloud
* MS Azure
* digital ocean
* IBM Bluemix (this interface is confusing, but with little bit of effort you can set it up)
* softlayer (cancelling your account is difficult and the interface is also confusing. But the helpdesk helped me with cancelling the account. So no problem here. They even let my vps running for weeks after cancelling)
* VMware service was too complicated. I didn't get it working.
* vpsie
* vultr
* cloudsigma was also too difficult to setup (they also use VMWare I think. The problem is I wasn't able to make a network connection.).

I didn't have any credit card problems with the above mentioned services. But if you test it, you should be cautious of course. It is important you search for reviews of the services you want to test to see what the reaction are of previous users

I decided not to test the following: Oracle, HP, fujitsu, linode