To be a Town Planner you're best off taking a course from an RTPI accredited course at university. I was doing a town planning course not accredited by my uni and was not sure if this was for me so I did a Geography degree. With a Geography degree alone it is possible to enter transport planning but it is difficult. However, someone from my course got a job in that area. I am looking for a career possibly in this area and had an interview for a graduate scheme but was unfortunately unsuccessful.
In terms of salaries just take whatever you can to get your foot in the door, once you have proven experience or become a senior planner then thats when you'll look at a high salary.