Users start with 3 giveaway slots. If you really want to stick with your own rules, this may be your final one
(deleting a GA does not return the slot)

The storyboard of a giveaway is pretty simple:

1. GA creator creates a GA
2. Users enter the GA
3. SG draws the winner(s)
4. GA creator sends the gift(s) in 7 days
5. Winner(s) activate the gift(s) and mark it(them) as received

If step number 4 does not happen, winners can mark the gift as not received starting from the 8th day (the option is simply disabled until then). EDIT, just a bit of clarification: winner can mark the gift as received any time, even after having it marked as not received for some period

Some of the things which are not part of the process

• Winners should not mark a GA received prior to successfully activating the gift in their Steam library as it may result in a suspension (see bottom of Roles, linked from all SG pages: "Not Activating Won Gift - 5 days")
• Winners are not obliged to subscribe YouTube channels, or fulfil any other requirements of the GA creator, with the sole exception of pack management (e.g. when giving away GOTY, collector editions and similar packs, GA creator can decide to accept/reject winners already having some items from the pack, for example the base game)

More about SG: FAQ link above, and guidelines (this can be easily found from the FAQ page)

I suppose...