As of 2015-05, SoulseekQt doesn't have built-in options to 'Autostart with Windows' and 'Start Minimized to tray or taskbar'.
Luckily, both options are available externally and offered by Windows.
1. In order to make SoulseekQt autostart with Windows 7, put SoulseekQt shortcut to:
2. In order to make SoulseekQt start minimized, right mouse click on SoulseekQt shortcut - Properties - select Shortcut Tab - Run: from dropdown menu select Minimized - OK.
3. In SoulseekQt go to Options - UI - check 'Show tray icon'.
By using 1, 2 and 3 you can make SoulseekQt autostart minimized to system tray.