I started with an agent to get the Vetassess part, which they did really well, but as we started to prepare for the EOI I wasn't happy with how they were treating us so decided to go it alone.
To be honest its not to bad, the most important part is getting the EOI points right, the actual application after is pretty simple as its just filling out your personal information and uploading the documents, and this forum helped me out loads in getting it all together, We're right at the end now just waiting on a Vietnamese police clearance which is taking forever! but the hardest part of the whole thing for me was the vetassess at the beginning so much paperwork and running around getting statutory declarations etc...
You're claiming 30 points for age, 20 for english and 10 for qualification, I'm in almost exactly the same situation as you apart from different trade and losing 5 points due to my age therefor 190visa. I'd worked as a sheet metal worker for 5 years and never been qualified, I was originally going to use this for 5 points but it wouldn't have counted as I wasn't "skilled" As ABG said in a previous post they count work experience as on the job training for unqualified people, but if they've given you an AQF3 thats a 4 year course, so you lose 4 years work experience.
Make sure on the previous employment section you mark all of it as "unrelated employment", or it will give you points. The worst thing you can do is over claim points (well ticking yes on the "are you a terrorist?" question is probably worse). Not claiming work experience makes it loads easier as you only need to upload: skills assessment, AQF3 certificate, PTE results and passport/birth cert to get the points!