The metrics you cite are performance constraints - you're not measuring the server performance - although having said that, there are very few Nagios plugins available off-the-shelf for performance monitoring.
I would suggest Nagios as the tool for measuring and reporting performance problems - but you say you've already got it installed but "it is impractical to open SSH console running top for each server." - this doesn't make a lot of sense to me - Nagios is specifically designed to do that for you! Have a look at NRPE for details of how to manage monitoring from a central server.
"Disk space issue" - in the standard nagios plugins
"Resource Hog" - that's a rather meaningless metric. You can get current/cumulative CPU and memory usage, # open files and other stats per process from the /proc filesystem - wrapping them in a a script to create a nagios plugin is trivial. For measuring per-process disk I/O, this was always a bit of a problem on the 2.4 and early 2.6 kernels - but I understand its now possible in more recent kernels - see iotop for an implementation in Python.
"Failed root / sudo login attempt". As I've often said in the past, most of the security stuff written to logs tells you where the security is working properly - i.e. most of it is of no interest. The important things are where your security is compromised. What you should be looking at is successful root access. Nagios has plugins for log monitoring.
"Anything else" - well yes, performance monitoring. There are tools for injecting transactions on various services available as plugins for Nagios, bit without knowing what services you need to measure its hard to be more specific.