Just bought Disco 2...already having problems

So I just bought my first Land Rover, a 1999 Disco 2 TD5 not two weeks ago and within two days my ACE warning light came on (after the first right turn), my heater doesn't blow hot air, and my coolant level in my expansion tank dropped significantly. I need help! I am currently a jet mechanic so I'm not bad at turning a wrench, but unfortunately I don't know much about cars. Anybody got any ideas before I go get gouged at the garage?

1. What ACE light... amber or red? ..anyway for this one the best is to read the fault code...if it's amber watch the tank to not go empty and u can drive it untill u get near a helpfull chap with nanocom or hawkeye....the ACE components are not cheap so to start replace parts based on luck or guesses is not an option

2. The cooling system must be free of air and properly filled with coolant... top up coolant, warm up the engine then undo partially the bleed screw and wait untill no bubbles are showing there...make sure that the tank's cap is fully tightened. Watch for leaks.

The ace light goes straight to red...checked the reservoir and it's a little below min.

I will give the cooling system a good bleed and see if that helps...could that affect the heating in the cabin?

So for ACE refill the tank and read fault codes ASAP, and if the heater matrix is airlocked(or clogged) u'll not get heating

Ok so i couldn't find a place nearby that sold the proper ace fluid, so I drove it straight to the garage and they had the fluid there. The mechanic hooked up the computer and a bunch of faults came up...unfortunately he cleared them before i could write them all down. He said to top up the fluid and see if the light comes back on. The good news is that I drove for about 25 mins back home with no light...but the bad news is that the fluid level dropped again so there must be a leak somewhere.

On a lighter note, after I topped up the coolant and bled the air, the heat was blowing out. There was an odd gurgling sound coming from behind the dash when I accelerated though.

So I guess I'll set up an appointment to figure out where this leak is coming from unless I can find it myself and fix it.

Question...when are you supposed to check the ace fluid, cold or hot? Reason I ask is because when I turn the motor off and it's still warm, the fluid level is way low...but when I check it cold it's within min and max. Maybe there is just air in the system? Is the fluid level supposed to drop below min while the system is operating? If so, then there might not be a leak and the warning light was just an anomaly, and just needed to be cleared. Either way, the light has not come back on.

Sorry for being such a noobie.