Random thought: if I win giveaway and later make same giveaway, legal?

yes...

It's fine.

..... No, of course not. You activated the game that they gave you and then you bought one to return to the community. That is completely fine.

As long as you redeem your win, absolutely nothing wrong with that. You might want to make a NOTE (edit: in the new giveaway) you redeemed your win and that this is an additional copy. That would be a good idea to help keep the mob at bay.

It may come under some scrutiny but it will easily pass if the game is in your library.

It's fine as long as you have already activated it on your steam library.

i think its ok

Nah, that's fine, so long as you have redeemed it AND added to your library, its ok to buy another and give that one away.

and add a note to the giveaway saying that its a new copy and prolly add a picture of it.