Usually I see projects giving out 1-2 percent of their total tokens.
1-2 million in your case.

You can include bounties in there and airdrops.
If you want you could just directly let them join a telegram group then conduct a sign up method without taking too many information.
Just an e-mail and ERC20 address will be fine.
Take the total number of participants then divide it by how much you are offering.
They do that way back. Just telegram. But now, they prefer maximizing it for other campaigns. i.e. social media