About making a giveaway for a game prevoiusly won

yes

A few months is not a problem at all. But be careful if it is only a few days. Some may assume you are regifting. Happened to me. I always sit on duplicate keys for games I've won recently for at least a month. (Plus, they could also use SGTools at this point. But if only a couple of days, even I'd assume it's a regift and not waste my time with SGTools.)

Yes. As long as you have a copy on your steam account, it means you have redeemed your win, and you are gifting another copy.
(well, except if you manage to enter GAs, then have it another way and not sync, and then win it and make things look like the copy on your steam account is the won one.)

No problem.

Be sure, you can. After giveaway 5 copies of same game, CV is getting lower.

Yes there is nothing wrong of doing it :)

When you activate your win to your own account and mark received then you have nothing to worry about when making a giveaway with another key of the same game.

Here is a personal example to illustrate:
https://www.steamgifts.com/giveaway/euWFy/deponia/winners
https://www.steamgifts.com/giveaway/edNou/deponia

Ok, thank you all for your replies =D