Sir,
I am a fulltime Linux system administrator for a French ISP & Hosting company.
I've been using Linux since my teenage, began with Debian, used Gentoo a bit for fun, before going back to Debian/Ubuntu.
I'm really interested in security. I take part into CTF competitions, as well as bug bounties (reporting security issues for money, to companies).
I have my own roadlist of security steps I take when installing a server, that I based on CERT's PDF full of advice.
I will make your system secure, hardening systems is really something I like to do.
I will be able to complete your task list.
For firewall, I know a really nice frontend to IPtable is more userfriendly than their CLI counterpart.
For an antivirus, clamAV is pretty much the well updated antivirus for Ubuntu.
I'll be able to identify process that you can stop to gain more RAM.
Rkhunter, chkrootkit, are two tools I oculdn't live without (and strace / ntrace ;)).
Can you please PM me ?
I'm confident I can do this quickly.
Regards,