This TAK Best Practices guide from MyTechNet discusses how to secure your system from multiple levels Some of these are what I’d think of as user best-practices (e.g. use a VPN and SSH), but it also goes into ports, firewalls, certificates and some other topics useful for securing your system.
There are also several other solid In-depth articles on Building TAKServer from an RPM installer (its got an RPM install — Awesome! OMG that’s an involved process. frown), managing users and groups in TAK among others. There are a total of nine TAK-related guides and articles there right now.