Here are some thoughts on preparing for the main net launch of EOS using the EOS BIOS tool.
Do they fully understand the boot sequence ? Do they understand all actions that need to be processed in order to have a chain that qualifies as mainnet. (they decide on boot_sequence.yaml)
In EOS BIOS, boot_sequence.yaml is a declarative file that is stored on IPFS. It’s part of the target contents defined in my_discovery_file.yaml, the file that each node uses in order to broadcast their own infrastructure details. See the following documentation by 
BIOS Boot Sequence Tutorial: https://github.com/EOSIO/eos/wiki/Tutorial-Bios-Boot-Sequence
BIOS Boot Tutorial script: https://github.com/EOSIO/eos/blob/master/tutorials/bios-boot-tutorial/bios-boot-tutorial.py
It's possible to join the EOS BIOS boot process without using the tool as well, by pushing a discovery file to the "disco" smart contract. More details here: https://github.com/eoscanada/eos-bios/commit/fc213532f3938f8bd5fa61f8cb5844fd927cdfa6
Can they compile system contracts and compare their source code, making sure that the proposed contracts are legit, and do not contain rogue code?
This involves making sure you have independently verified the validity of the system contracts. One method for doing so is by grabbing all of the target contents described in the latest version of the discovery file you are using and cross-checking them against your own compiled system contract files. You can compile cpp system contract files using the eosiocpp program.
Do they understand how to make sure the snapshot.csv is valid, up-to-date and reflect the last Ethereum snapshot ? (they decide on snapshot.csv)
Steps to verify the EOS ERC-20 snapshot:
Step 1: Set up the genesis tool pre reqs (MySQL db, Ethereum full node, nodejs) https://github.com/EOSIO/genesis
Step 2: Run the genesis app for the latest period to index the EOS ERC-20 balances deterministically. This can take a while to index for the first time. The output will be a snapshot file for the configured period.
Note: if you get a bug about Web3, change the path to the ipc device in config.js to be absolute.
Can they properly boot the network and have they practiced being the BIOS Boot node?
Join in the staged launches happening in the EOS BIOS Boot channel here: https://t.me/joinchat/GSUv1UaI5QIuifHZs8k_eA
Coordination usually occurs through Zoom. You can also ask for an invite to the current staging area here: https://t.me/biosbootonboard
If you’re elected as the boot node, you’ll need to make sure your boot hook is prepared to perform the necessary commands and validations.
https://github.com/eoscanada/eos-bios/blob/master/sample_config/hook_boot_node.sh
Can they properly boot a node and mesh into the network, have they practiced join ?
Craft the join network EOS BIOS hook to call your own deployment scripts. Make sure to add your own key pair.
https://github.com/eoscanada/eos-bios/blob/master/sample_config/hook_join_network.sh
Also, it may be helpful to kick off some additional commands when the launch process is done, such as regproducer:
https://github.com/eoscanada/eos-bios/blob/master/sample_config/hook_done.sh