@MLBS No, you only get a bridging visa once you lodge a substantial visa application (like 189/190). Your student visa is typically valid 2-3 months after the end of your course, so you have to lodge a substantial visa application before the student visa expires. If you plan to lodge your 189/190 after your studies, your BVA won't give you the full work rights (you'll be stuck with 20-hour fortnightly limit).
The BVA takes effect as soon your student visa expires and until your new substantial visa is granted. For example, if your student visa expires in September but you applied for your 189/190 around August, your BVA won't be in effect until September. The validity of the BVA depends on when you'll get the PR visa grant.
I've asked around in the forum about the requirements for 485 visa, completion letter and academic transcript daw from the school ang kailangan (I'm still a little hazy/unsure if kailangan ang skills assessment pag Diploma ang tinapos mo, if degree hindi ata kailangan). Some schools kasi during graduation lng nag-iissue ng degree diploma, which could be 4 months after you complete your courses (so expired na student visa mo by then), so schools issue Completion Letter declaring you've finished your program.
What are the potential occupations for people who finish the Work, Health and Safety course? Check its ANZSCO code, and compare it to the ANZSCO code of your occupation (where you have experience). It could be considered "closely related" if the first four digits are the same. For example, if your previous work experience was under 233411 (Electronics Engineer), your nominated occupation's ANZSCO code would ideally start with "2334." Beyond that, you might have to inquire with the Assessing Authority about this.
Sorry, ngayon lng nagsink-in sa akin yung sinabi mo na fallback mo yung bachelor's degree ang basis for your 189/190 application. hahaha. kala ko mag-aaral ka uli ng another bachelor's degree kaya nagcomment ako about the 3 years of additional study. hehe