If you have an internal HDD, no real need to use a USB stick.
Internal HDD will work with EPG, timeshift & so on.
Flash should have enough room for picons depening on your needs.
Is it a good idea to put your picons on flash even if you have enough space ?
The EPG is actually held in RAM and only saved to it at shutdown or loaded from it a boot up (or saved at intervals if you specify in settings). No disk activity required normally to scroll through the EPG. Picons should not be stored on the HDD as they are loaded as required and not cached and will cause disk spin-up as @jukkal has indicated.
Ok thanks what location would it be i.e etc/enigma2