Are my electrical faults linked?

HI all, just wondering if someone could help with some issues on my girlfriends Fabia 1.4 8v comfort (51 reg)

Problems are electical:

N/S speaker sound alters randomly, i.e tinny then more bass/muffled. (oe tape deck)

Heater fans randomly have a "turbo" boost for a split second (A/C works fine and flaps are adjusting normally)

Headlights and dash illumination inc mileage flicker intermittantly (have replaced battery)

Temp gauge was dropping during driving but i replaced the coolant sensor and that is fine. after replacing that the coolant warning light kept coming on but i fixed that by topping up coolant to just above max.

Lastly the steering warning light comes on intermittantly with no loss of steering assistance (have replaced battery). This can stay off for days, no pattern.

Have trawled the forums and have seen similar faults and i am wondering if i am dealing with lots of different faults or 1 big or hopefully minor problem.

any advice would be appreciated.

Monty820