1) Coinkite uses addresses of the form "m/n" where 'n' goes from 1 (IIRC) and counts up for each transaction (or change) in the account.
Previously-used addresses are easily found in the "audit report" which you can generate on the detail page for the account. In fact, the subkey is a column there as well.
2) Sorting of the keys (which happens after they are mapped from BIP32 into normal bitcoin addresses) is lexicographical sort (IIRC) and is compatible with how ms-brainwallet works. You should be able to generate the same keys using that site.
As for Electrum, I haven't tried to get it to interoperate with Coinkite yet.
I am playing with ms-brainwallet http://ms-brainwallet.org/#generator
I generated 3 keys from coinkite keygen, and if I place those xprv private keys in the same order, it is generating me different addresses.
Using these 3 xprvs:
1: xprv9s21ZrQH143K3T9wwvn4rHVK8pbkWxUEwJJTvysJJLSdaeLtJTqY64dRcn9v75CSzTgmQT8AUzg KbHrawDaVR9n5KD2VfEfL5Utmr4eLdbz
2: xprv9s21ZrQH143K48EpkMW6MAHPRya9nYtV1M73z7jLqpgCd4F5TZZkiqFpXMakGnTesAKuQfra1im J79UkXtyaAbj6kxhagTg2eMYy5cUKkx6
3: xprv9s21ZrQH143K2bQ5qvK4iHykpBAWyq8ktkPsVb2gU6boGUwvRufSJFkbzsYu7zjmewq7prRYPgZ TPHJKeb26sxwy9iD3LDUHk3EgDWYeQJX
ms-brainwallet generates the address 33BFPWemAkJTg2CZE3EfZzkrvABC7g6DrF, but in my coinkite account it shows 3PXecgTTyQ1twbPhqsMxcz71sL1ACKwm6X
On ms-brainwallet, if I use the extended public keys on the create tab, manual, enter them in order:
1: xpub661MyMwAqRbcFwER3xK5DRS3grSEvRC6JXE4jNGurfycTSg2r19ndrwuU2dCHtzycanQk7eyq2s x5XcLJJw1Uqmce7rq2FeD2E1svpEx4uu
2: xpub661MyMwAqRbcGcKHrP36iJE7z1QeC1cLNa2enW8xQADBVraE16t1GdaJNbQBKMG5vmtt47saosj sk54mhVnbiqqyGyM7oWZkbhXkokdXkUd
3: xpub661MyMwAqRbcF5UYwwr55RvVND11PHrcFyKUHySJ2S8n9HH4ySygr455rBhrn518vo656tkpAz3 XPk8afjmFc857qhUwA5NrpeC8kd8fwog
It will generate the address 3FK2DK2KC6KU9FwP845jAKdqxTCorhBVyp
But it doesn't match with coinkite address. My goal is to recreate the coinkite address, without using coinkite.