I read somewhere that using a dedicated server, we will have to be responsible for its security and system updates. Is it right? If so, how complicated will it be?
it is highly recommended to consider Managed Servers. Bodhost provides Managed servers and takes full care of server security and system updates.
Server management includes security monitoring, installing, compiling and maintaining the standard server application/software package, latest security updates, technical support for server related issues, and more.
I find that it's always best to go with a managed server, just from talking to people. I have loads that I'm still learning though, so perhaps if you have more experience, you'll just do it on your own.