This guide is pretty good. To get a chance for many airdrops, may need about 10-20 $Inj tokens, but even a couple of $Inj tokens would get you a good chance of at least 3 of these airdrops
The mere staking of $Inj tokens on the network and picking the correct validators would get you 3 airdrops, plus a lot of projects don't even require specific validators, so pick Talis and Black Panther, divide your Inj stack