Which Derailleur for Trek DS 8.3 Gary Fisher edition

Hi,

I own Trek DS 8.3 Gary Fisher edition since last 5 years.
Yet, I am a beginner so need your help to fix my cycle.

I am not sure if it is 2014 model or 2013.
As per spec sheet, I can understand the difference is in 
Cassette:
2014: Shimano HG31 11-32, 8 speed
2013: Shimano HG31 12-32, 8 speed

I don't know how much difference it make when I am choosing my Rear Derailleur.

Crank is Shimano Acera M361, 48/38/28 w/chainguard.

Now, original one is with Acera Rear Derailleur and I was looking for replacement as on ameture mechanic spoiled it by welding a hanger instead of fixing it (I know it is very strange but, I am not able to remove that additional piece fixed to derailleur).

Will Acera M360 be suitable for any of the Cassette, 11-32 or 12-32?
Can I go for Acera RD3000 SGS Long 9 speed also and later change shifters?
Hanger will remain same in each case or will change?
Does Crank specs have got anything to do with Rear derailleur?
Current one on is Shimano Acera M361, 48/38/28 w/chainguard.

Thanks