A/C Problem: e60 AC delays & blows Super HOT in the Desert!

[domluv]

Hi good people of the BimmerWerkz community...

I recently purchased a 2004 530i for work (98k miles), I suppose it's an e60. It's my first ever BMW and I am not a mechanic. I've already spent too much money fixing random things (about $2000 in 2 months) and problems persist. (I'm tempted to hate the Ultimate Driving Machine, but certainly hate the prior owner and BMW dealers already )
A light comes on for increased emissions, and the mechanic says it might be a leak in the gas line from a definite prior accident. Of course the prior owner claimed no accidents. The gas tank doesn't have pressure when I open the gas cap to refuel. Estimated fix cost: $200-1200.

But that is not my biggest concern...
I've had the same problem as others where the A/C does not engage until after ten minutes of driving or so. I hear the engine working harder (maybe the fan) and sometimes the A/C seems weak altogether. I had the freon replaced completely based on the mechanic's recommendation but that did nothing except cost me money. I live in hot and sunny southern California and recently went out to deathly Palm Desert (110+ degrees F). If I parked in the sun for 10mins or more, the A/C blows extremely hot air, nothing cool at all. I was there for 3 days and drove with all the window down for air the whole time but it was still unbearable for me and all passengers, especially in a Black BMW. This is a bad problem as I travel far and a lot to hot desert areas to meet and drive clients around.

In addition, when I go to cold climates like the mountains, the heater delays or sometimes just blows cool with no heat at all. What the heck?! Is something inverted? Did I buy a demon possessed ride?

I feel so stressed and dismayed! The First mechanic says it's definitely the AC Motor ($200-400 job) and if I run the AC in hot temperatures, it can fail completely, seriously damaging the engine by killing the water flow. The Second mechanic who changed out the freon (r134 or something) says there is no AC Motor, but an AC Compessor ($1200+ part) and that the First mechanic must be talking about the water pump. The Second mechanic now suggests replacing the AC Compessor/ Unit itself, but that's a $1600+ deal with labor. He says it's gotta be a new unit, not rebuilt/ reconditioned.
To add insult to multiple injuries, the mechanic said I should have gotten a Lexus instead!

I tried to read over the forums, but I'm wondering if I have multiple problems or something unique. Please

Is it a Blown Fuse?
Is it the Temperature Sensor?
Is it the Pressure/ Expansion Valve?
Is it the Aux Fan?
Is it the A/C Motor/ Compressor?
This seems to be the order of costliness. I don't even know what everything is... but I'm not sure if the mechanics even know or care enough to figure the real issue.

Sorry for this lengthy message, but I wanted to detail the issues for my Bimmer MDs
Thank you sooo much in advance for your time and help!