To answer the question as to which aircraft to study depends on what is your final intention. If you just want to do an endorsement on a conventional aircraft then the B737 is the choice. However, if you would like to familiarise yourself with the latest fly by wire technology then the answer is the A320. The degree of difficulty in training on both is about the same, the difference is particularly noticeable in the operation. The simplicity of the A320 cockpit and the FBW philosophy make it a very simple operation when all is going well, unfortunately when things are not it can become a handful. Getting a course shouldn't be to difficult.
As far as line training is concerned, well that is another question that and I'm afraid I have no suggestion. In fact as intimated earlier, it might be very difficult. Even to work without pay as has been done in the past to get the experience dosen't happen anymore.
Have a nice day