1. Yes, in fact you can have a VPS and a tommy account simultaneously.
2. Debian isn't a common OS that users order for a VPS so we don't really add a new release unless necessary (such as an OS going EOL). Ubuntu is recommend because it's more user friendly and easier to use than Debian, also with Ubuntu it will install itself unlike Debian which requires a manual build which can take a while depending on what time you order the VPS. AlmaLinux is the only other self install OS
3. Yes you can change the OS at anytime.
4. Yes as long as you are not sending spam or anything.
5. Yes, you will be able to upgrade by clicking the upgrade button of your VPS account on the heliohost.org page.
6. The VPS would try to renew on the due date. if it fails, we'll let it retry for 5 days then on the 6th day, we'll email you and ask if you would like to setup a new subscription. if the email is ignored, then the VPS will be shut down and we'll hold onto the data for 36 days in case you would like to come back. if you ever need more time to make a payment, we would be more than welcome to give you an extension until you are able to do so.