Best thing to do for now is depending on what you want to colo your server for like hosting for others or personal use..

Figure whats best for you a Gbps line shared or dedicated or something smaller..

If its hosting for others then what ever money your gonna spend like enci said find a top notch cheap vps provider to host your main site on then from there decide how you want it all setup..

Debian id say in my own experience is the best os but most use centos because its the hosters default..

Security measures to look into are securing your web server and find a firewall to help you to help against ddos..

Most of the time for shipping i like to advise to always pack your server with very very good box cushion because those people who handle the boxes are assholes.. always remember to mark it as fragile for a just in case..