Can I use a VPN and Proxy at the same time?

I want to a VPN for my computer. From my understanding, the VPN changes the IP address of the entire computer. Can I then configure firefox to work with a proxy so that I can use an IP address that I can change from time to time?

I'm planning to change my VPN twice a month and my IP address in firefox once a day.

Does this even make sense? I'm a novice.

Yes, of course you can. But it is a little slow.

I dont know what you want to do. To just change your ip adress it works, but remember that your vpn provider can theoretically always see your traffic..

Yes, this works - you can even tunnel VPNs over VPNs if you're so inclined.