Can you delete a managed release package if it is not installed in any subscriber org?
Yes, if you can get it uninstalled from all subscriber orgs (including any sandboxes, etc), you can delete the package entirely. I've personally done this in one of my developer orgs a while ago.
After deletion of managed release package, can you re-upload the package as a new release package from the same or different org?
You can create a new package and select that as your new managed package. You cannot migrate your namespace to a different developer org, so you're stuck with the org you have, unless you want to create a new namespace.
Can I have multiple managed release packages for the same code base in different orgs? Would that cause any problems?
No, a namespace can only be uploaded from one org, and cannot be removed or migrated to a new org. As such, you can't have multiple releases in different orgs. All releases must be in the same org. You can upload as many versions as you'd like.