I have a single wallet running as a masternode.
Can I create different addresses on the same wallet, and store my coins on it?
If I send more coins to the same wallet, but to different address, would it stop acting like a masternode?
You can have as many address in your wallet as you choose, but you can only run one masternode per unique IP and or wallet. if you choose to run more than one masternode, I would suggest using the Controller Wallet/Remote Masternode setup that is listed in the OP.