What is the downtime threshold for a validator before it is slashed?

Additionally, how are complaints submitted and voted on for malicious behavior? Is that an automatic process? Or does each validator need to manually vote on complaints that are manually submitted by other network participants?

Also, is it required to store the wallet for a validator node on the machine? This seems very unsecure

That's why there is single-nominator contract that allows to store most funds on cold wallet.

Can you link me to this? It seems like the validator would still need 600k TON of self stake before it can receive nominators. Where is that 600k TON stored?

Also, is that 600k TON required as self stake? Or can it all come from nominators?

I still would love to see what this single-nominator contract you are talking about is. Is it this? https://github.com/EmelyanenkoK/nomination-contract/tree/master

But if I want to use a restricted wallet so that the owner of the TON can be a cold-wallet, is there any documentation on how to use a wallet not created by mytoncore?

https://github.com/orbs-network/single-nominator