EMS Light intermittent - Air Mass Meter/breather pipe

I recently purchased an x reg 2001 a3 1.8 t sport, private sale.

the ems light came on the day after i bought it. it hadnt been on when i test drove it, when the rac checked it out, or when i drove it 50 miles home after i bought it. The light came on the following day.

i had it checked by the main dealer (yes, i know, mistake!) who plugged it in to vag com and said it was due to needing a new air mass meter , and a faulty breather pipe (sorry i didnt get the actual numerical codes). since this work was going to cost 300 inc labour at the dealer, i thought i would shop around.

before i got the work done, 3 days later, the light went out, and it stayed out for the next two weeks - driving it short journeys every day.

I did a 150 mile round trip this weekend - drove like a dream.
then on monday, EMS light comes back on again. it goes out again four days later - so its off at the moment

my questions are these:
1. the car drives well even when the light is on - any symptoms i should be noticing with those faults?
2. am i doing any damage to other engine parts/systems by my "lets just wait and see" method?
3. im sceptical about rushing into changing parts when the light goes on and off - reading these forums shows that it often isnt the first thing they change that fixes the EMS light problem. Any advice people can give on this? so how confident can i be that the error codes that come up, are the real problem? could it be the sensor?
4. where is the breather pipe and is it easy to change myself? (i think i can change the air mass meter/maf myself)
5. could it be anything to do with the lambda sensor?

thanks for your help in advance