Hi Jettesen.
Iwould be a bit weary of going to BA LGW. You will work to the 'EOG' or eurogatwick contract. Flight pay is hourly rate and there aren't many night-stops any more out of LGW. Can you not go ask to go 'on the list' for a LHR course? Then maybe join easyjet in the time you wait?
On the plus side, LGW short-haul will be merging with LGW long-haul over the next two years so you would have mixed flying albeit on a 'new contract'.
Friends say you can expect to take home around 1100-1200 per month after tax. LHR short haul between 1600-1800 provided you do 'trips'. More with overtime. Hope this helps!