With Windows 8, the start screen is a set of tiles that are simply shortcuts to your programs which, combined with the menu that pops up when you right-click at the bottom-left of the screen, means that you don't need a start menu button on the desktop. With 8.1 there is a setting to go avoid the start screen and go straight to the desktop at boot up, and in the update next month you won't even need to set that because having a touchscreen will be detected automatically.
Running a program in W8+ is no different to running it in XP and overall you should find that everything runs that bit quicker.
Some people are obsessed with having a start menu button on the desktop taskbar and if you are one of those then you should perhaps go for W7 although there are 3rd party programs that will give you one for W8+.