How many games can each lvl give away?

You'll need to send in a ticket to support in the "Other" category, explaining your situation.
They'll set you up.

The number of games you can give away is not based on level, but previous number of games given away. For every 3 games you give away, you'll get another giveaway slot. But for big givaways like what you're planning, you should do as Tzaar suggested.

I think the maximum number of games you can give away at the same time is 300 unless you ask to support.

You need to contact support to increase your giveaway slot.

From FAQ

I'm a game developer or publisher looking to promote my game through giveaways. How do I get started?
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... If the limitations on your account do not allow you to create a giveaway for 50 copies or greater, then please contact support. We'll upgrade your account to developer status, allowing you to create giveaways up to 100,000 copies.