Actually it depends on what u are going to study for your degree level also. besides that;
$$ = STPM cheaper , A Level expensive unless you get full scholarship.
duration= STPM longer , A Level shorter(something like that)
Local Uni= STPM yes,but depends on your result
Private College/Oversea= Choose A Level
Well, it depends on your choice actually.hope it helps and good luck.

Pengajian Am is compulsory subject.
Minimum 4 subjects
maximum I dont know but mostly 5 subjects
Then how thick each subject's text book? I would say it depends on which subject.
for example, if you take sejarah,then you need to study 4 books.