Lets say someone buys a server or a vps, before hosting a site on it, we will need to do a list of things to secure things such as close ports, enable su access for shell and stuff. Could everyone reply with the security measures that need to be applied to make your sites and database safe and make it hack proof?
There is too much to list. You cannot make a server " hack proof " you can make a linux server aware of being attacked, and it will take action automatically to ban those attacking it. Using your self-assigned intelligence, you can seek your own answer via a simple google search linux server security guide not hard... or HIRE a Server admin, no stress, no hassles and you can blame someone else if the server gets hacked
Well as for a list thats a pretty tall order bud but may I suggest you install Configserver Firewall http://www.configserver.com/cp/csf.html When you run the sceurity check it will list many things that might not be secured and telling you how to secure it. It wont secure everything but its a good start
Are you going to be running a control panel such as cPanel/WHM or LxAdmin? They both have features in place, LxAdmin is very secure because it uses Lighttpd you will have to spend more time on cPanel/WHM because it uses apache, installing things such as BFD... I will post some tutorials some time in the future Just look at google on how to secure cPanel... etc