Is it better to split your btc into multiple addresses in the rare case one gets hacked?
Also, if one of your addresses did get hacked and all your other addresses were associated by having been generated from same seed, are your other addresses at risk (assumming they did not figure our your seed of course).
First, addresses don't get really 'hacked'.
In order to spend the funds lying 'on an address', the attacker needs to get access to the corresponding private key.
Now the question is, how does the attacker gain access to the private key ?
If you have your funds stored on a desktop wallet and the attacker gets access to your computer (e.g. via malware), he will have access to your seed (which will lead to all private keys being known to him).
If somehow the attacker does get access to only one private key (which will only happen in very rare cases where you store the private key seperately somewhere or accidentally give it to someone), only the funds associated with this one address will be at risk (i.e. stolen).
Just to make my statement correct:
If you are using unhardened paths (which is not the case in most wallets), 1 private key AND the public master key is enough to calculate all other private keys of the same derivation path.
This mostly won't affect you, but it is worth to be noted.
Do you feel it is foolish to keep too much btc in any one address?
No, definitely not.
Feel free to store as much as you want on a single address.
3D2oetdNuZUqQHPJmcMDDHYoqkyNVsFk9r for example, is the address of the Bitfinex cold wallet and is holding roughly 138k BTC at the moment.
