If I break the 24 word seed with 256 bits into two 12 word parts, can I safely store them in two separate locations like I can with the seed extension?
With a 256 bit seed, are my addresses and keys still the same entropy as normal?
Yes. When the number of words change (12 vs 24) the size of your initial entropy is changing and the only thing difference is what goes into the key derivation function to derive your BIP32 seed. After that everything else is the same, and bitcoin private keys only have 128 bits of entropy no matter how you create them.