Hi Julia,
Well those are all excellent questions. The answers vary really. As far as the visa process goes, the first place to start would be the Spanish Consulate General's office nearest you.
You will have to submit paperwork in person in Spain and then return to your home counrty while you await approval. The Consulate General's office will be able to tell you better about the immigration laws as they pertain to Australians.
As far as gettting certified at home versus abroad....well this is the subjective part. My opinion, go for the course abroad. There are many benefits to this. Such as, already being in-country to get acclimated to your new environment etc., the networking of other TEFL or TESOL grads that can help you with tidbits and leads, etc., as well as you can get an early jump on the job search while you're completing your certification course.
The way I see it, you're going to be dropping a wad of cash either way, why not do it abroad.
So there's my two cents for ya. Hope that helps.
Salud!
Michelle
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