Yeah you can manage 100% uptime provided you have a cluster of servers and the technical know-how to do it.

All I can add to this post is, looking after a dedicated server can be quite hard and stressful!

Some links you may find useful if you do decide to get a dedicated server are:

Common SSH Commands - Linux Shell Commands - Hosting Tutorials
How to install BFD (Brute Force Detection) - Server Security
How to install APF (Advanced Policy Firewall) - Server Security
Close Open DNS Servers - Server Security
How to move a large forum from Server A to Server B? - Hosting Technology - Web Hosting Tutorials & Reviews

Some of them may be outdated and based around Cpanel, but you follow the tutorials and advice and adapt it for your own needs.