It's a bug in the tezos-packaging repository. We have fixed it in the v7.1-2 release. Can you please try again with v7.1-2 or newer? You can run wget https://github.com/serokell/tezos-packaging/releases/latest/download/tezos-client to overwrite the version you have, it should work because it downloads the latest release (where the bug is fixed).
If you want to create private testnets, you definitely should look at tezos-k8s. It's an easy-to-use tool to quickly deploy testnets based on the Kubernetes infrastructure. Just follow the steps given in the link. Basically, a testnet on your machine could be associated with a namespace that contains pods. Each pod stands for a (baking or not) node, and each ...
Yes, the old testing networks are abandoned and brand new networks are launched using the new to-be-activated protocol.
For instance, Carthagenet will be deactivated on 12/12/2020. The current Delphinet test network will remain as a protocol copy of mainnet. Edonet was launched yesterday, which is using the upcoming beta 008 protocol.
As the error message quite clearly states, you need to stop the container and remove the lock file inside the data directory. Did you bind-mount external directories into your container or just using default storage? Please show us the entire command you used.
The error message is meaningless for a tricky reason (a fixpoint is badly computed leading the error reporting mechanism to raises an error itself: https://gitlab.com/tezos/tezos/-/merge_requests/1376 )
Anyway, the root of your problem is probably that you don't have the right activator key. The public key of the activator is defined line 105 of src/...