Same question, same answer
Yes. Remote nodes can track your IP address, in which case your privacy could be lessened.
If you feel, if someone might knowing your IP address, as a security issue, don't use remote nodes, or use VPN.
Yes. MyMonero is using a remote node. Anything not connecting to a local node, is using a remote node.
Note that communication ...
In both Simple mode and Simple mode (bootstrap) the GUI will automatically connect to a random remote node. This configuration was preset by developers in order to improve user experience for the less technically inclined. This further means that, in both these modes, users cannot set a custom remote node. Whilst this may change in the future, users ...
You might be using a payment id with your address which could be why you might not see the same address. To verify you can tell if the address is an integrated payment id, by see if the address looks similar. If it is, then you have it in your wallet. Also make sure you have your wallet fully synced too.