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Like maewert said. The Pi Zero wouldn't really be up for the task. However, if you feel like getting a fairly thorough knowledge with computer engineering, I have recently thought about engineering a new IO board for the RPi Compute Module 3 with stackable headers specifically for clustering units.
How To Make A Raspberry Pi SuperComputer!
Yea, then you'll be vulnerable to Firewall and NAT evasion techniques (such as Sami Kamkar's NAT pinning) and by extension Arbitrary Code Execution and Traffic Sniffing (in case you authenticate with Telnet which is unencrypted). Telnet needed to stay dead in the 70's when it was created. Go with SSH or better yet create a VPN on a controller box with decent quality encryption algorithm and key length and a thorough and restrictive firewall. Don't ever install a service that doesn't care about your security or you will have people farming out your resources for password cracking/mining or a botnet.