Re: Maximum length of visa extension
I don't think there is a maximum - but yes, 12 months is allowed. You can explain in your visa extension request that you're asking for 12 months to be able to become CL and later on apply for PR, and make sure that you include enough information about how you intend to financially support yourself (your partner I suppose will be the main responsible), and it's usually not an issue. A few people have been approved for 14 months on this forum when they stated that the waiting time for their VO was 14 months.
Good luck,
Sweden