@flabbygasted to answer your query,
<b>Also, do we really have to get a grade of 8 sa lahat ng category sa IELTS or band score would be considered?
</b>
Kung 20pts sa Language proficiency ang target mo, YES, you need to get an 8 on all bands. Passing is 6.5, pero walang points. 7 is 10pts. I repeat, ALL bands po ang usapan dito. I do not know though, if iba ang requirements pag Teaching ang skill.
<b> Kailangan po ba palaging related sa pinag-aralan or kahit hindi naman as long as I found a good job there?</b>
Hindi po naman required na laging related sa pinag-aralan ang job dun. You can take any job you like as long na qualified ka. For assessment purpose lang po na yung previous work experience mo ay related sa nominated work mo.