As per the above comments, the issues you mention are probably just down to old sensors. Temp gauge readings vary as the sensor ages, and are only relative. Its not a precise measure of your engine temperature.
If the cooling and oiling systems are allowing normal operation, then its all ok, and you dont need to spend any money. Keep changing the engine oil as frequently as you like without a flush, and it'll be grand.
If your particularly concerned about the oil pressure, either do a pressure test, and/or remove the sump to check the pickup gauze is clear.
Dont worry, something will go wrong soon enough that will require expenditure!
