Are you planning to get live plants? I wouldn't seed the cycle with bacteria yet.
It's a bit more complex than adding the beneficial bacteria from another tank and waiting... the beneficial bacteria still need a food source - something producing ammonia, and ideally enough ammonia to grow the bacteria colony large enough to handle the bioload of the new fish you plan to get.
Since you plan to do live plants, I would advice getting those first, get them growing, especially whatever fast growing plants you're intending to use, so that it's more of a silent, planted cycle. Once those are showing signs of growth, then seed the filter with BB from your established tank and add your first batch of nano fish.
Which species have you decided to go for? If it's a tiny species like green neon tetra or chili rasbora, then you could/should get all 12 at once, then as long as you fast and only feed them very lightly to begin with, between the growing plants and seeded filter bacteria, they should be able to handle the bioload, since it's very light with those tiny fish.
But I'm not a cycling pro by any means, since I've never had to cycle from scratch, and always had an established tank and growing plants I could move to start a new tank. Hopefully
@WhistlingBadger @Wills could give you some better info!