Hello epitome, I recently applied for this post and have been through part of the application process. The salary is fixed depending on your educational qualification and the minimum to apply is a diploma. Don't know if I'm allowed to share but generally it's on the higher side because of shift work and the amount of stress involved on the job.
As for the aptitude test, there's no way of studying or preparing for it. Like it says, it's an aptitude test; you either have it or you don't. It's ~2-3 hours long and tests things like your memory, thought process etc. so if you want to prepare for it, get enough rest the day before.
Provided you pass at every stage, after the aptitude test you will go for a first panel interview, an orientation of the facilities, and a final panel interview. Hope I helped
