Once a team successfully bid for a parachain slot, how long is the window that they can leave the slot empty? What will happen if they cannot successfully connect their chain in before the window closes.
Is there a more detail instructions on how a bare-bone shell parachain got upgraded to Statemint?
During the parachain upgrade, can the team reset the genesis block information?
I don't really quite get your question. One can bid for a slot as long as there is an ongoing auction. Once a winner is chosen, its parathread will be granted with a slot and then onboarded as a parachain. This parachain will start producing blocks as soon as there are a couple of nodes and collators running for it. And will keep on onboarded until the end of the LPs that were won during the auction. For a more detailed explanation on how auctions work please refer to the wiki - https://wiki.polkadot.network/docs/learn-auction Just to add here, there is nothing like that window you talk about in the implementation, so collators can be run anytime, but block production won't start until they are not running.
I think Bruno's comment answers this point by itself.
Thinking on an upgrade from shell to another runtime with more features, in that process you might need some genesis storage for a few of the new included pallets. You can add this storage items as part of a migration during the upgrade process.