Yes, do the GAPAN test. If you can't pass it you might need to reconsider your plans. Even if you get a good result, it doesn;t guarantee that you will pass the exams. The tests check your co-ordination, spatial awareness and multitasking ability. Also get your class 1 medical before you start training. If you can't get that, then commercial flying is a no no.
Not sure about sponsorships but I think many on PPRuNe are self sponsored and like me, up to their eyeballs in debt.
AP