the level should be about 9 inches down from the fill plug IIRC..Make sure the big hose near the pump is not collasping when its cold and sucking hard. this hose will get soft and collasp and cause the pump to starve when cold.
Also the relief valve will pop and cycle when extra cold as the pressure is high and the fluid is thick.
you can run hydraulic fluid or upgrade to "tractor" rated hydraulic fluid which will have a bit more additives, anti foam, and oring conditioners in it, so the tractor version is usually worth the bit more you pay. but dont buy it from a tractor dealer where its twice as high as from other sources. IE samsclub is always good. some walmarts and most auto parts stores will get it much cheaper.