I am linux developer . I read your requirement. I am doing similar type of work in my primary profile. Tasks like multi-level authentication, easy to use, listing on particular tcp port, secure connections, are very easy. And also the task which is related to configuration update of devices and monitoring/communicating with them is also under my scope. Since your project also need web development so it will take 15 to 20 days to finish.
Milestones:
1.> 25 to 30 days to finish primary task like monitoring various devices and communicating with them by tcp connection including security and multi-level authentication. ($4000)
2.> 5 to 6 days to develop GUI. ($450)