Captain R, I would work on AMSA taking 1 - 2 months to get through your Immigration Assessment. You should then get a letter of assessment which will allow you to book orals.
I got AMSA to certify the copies of my company sea service letters (the girls in the AMSA offices can certify these letters for you), they then scanned & e-mailed them to me. I was then able to send the scanned certified copies to Immigration for my visa application.
It's AMSA who have to verify your employment over the past 10 years too, there is no special application form (or fee) for this, just send all of your evidence to Seafarer Standards in Canberra along with a cover letter explaining what you're after, and be prepared to wait for another 1 - 2 months!
It's a good idea to get the IELTS out of the way early too, it took me a couple of shots to get a band 8 in everything (bit harder than you may think!), and with the SkillSelect system you really need as many points as you can get. Good luck with it all, if I can offer any help or advice at all, just give me a shout.
Rich T, I think you may be pushing it to get your visa application in before July - the problem is the AMSA factor, they do everything so slowly. You could be waiting 1-2 months for your skills assessment, then you have to book orals & medical, and even after you pass the orals they take another month or two to send you your letter of Positive Assessment allowing you to apply for you visa.
Get evrthing done as quickly as you can, and you may stand a chance. Good to see you've booked IELTS, and apply to AMSA soon for employment verification too, as they will take time to respond to that.
The visa is valid for 5 years, but you have to activate it within the first year - that means everyone on the visa has to clear Australian immigration before the first year is up, or the visa expires. Could mean quite an expensive holiday if we can't sell the house or line up work before then!
As above, if I can give any help or advice, just give me a shout. Good luck.