To answer your first question: no, you won't lose any programs or files if you decide to upgrade to Windows 10. You have the option to keep all of them (or none of them) when you upgrade. However, it's recommended to back-up all your personal files to another storage media, should anything happen during the upgrade and your files becomes inaccessible.
As for your second question, Windows 10 look and feel is closer to Windows 8.1 than Windows XP (obviously). It'll be easier to use for you since the Start Menu have been added back, so you'll feel a bit less loss because of that. If the Start Menu feel and look doesn't suit you, there's always a possibility to install Classic Shell and customize it so it looks like the Windows XP Start Menu. As for the rest, if you use Windows 8/8.1 regulary, you'll be able to navigate in Windows 10 as well. If you don't want to get loss, keep on using the Control Panel instead of the new Settings menu.