There is no level requirement if the CDQ is to move to a restricted class or PrC. The level 10 requirement (or alternatively, the 3 months' activity requirement) is for CDQs for all other personal goals, like joining an organization, etc.
Unless you were thinking of a different reason, I see no reason you shouldn't be able to submit in the Character Submissions forum at any time (for the secondary class), then take a CDQ with a GM of your choosing. You should choose the GM yourself, though--I recommend reading through their threads and choosing one in a good timezone who sounds like they have a style that would work for you, or thinking back to different quests you may have been on and choosing a favorite quest GM.
Hope this helps,