1. I'm not sure what you mean by "escrow form." In plain M-of-N the public keys are known to the network when funds are sent to them. In P2SH only the hash of these public keys is known. To create a Tx that spends these funds, one must know which public keys those were and also sign with the private keys. One person could collect public keys and create a P2SH address in which the other public key owners don't know about each other. The would have to trust this person to not create a different P2SH address and all owners would find out about each other's public keys when funds are spent from that address.

2. In plain M-of-N, the public key is known. In P2SH M-of-N, one must know the public keys to spend the funds. If you have a list of possible public/private keys, you have to try every possible combination. You don't even know what M and N are. This is why users of P2SH need to also store the output script (which contains the public keys) for that address.

3. They are trying to create an output script, which has public keys in it in some order, that hashes to the P2SH address.These keys are not publicly viewable on the blockchain unless funds have been spent from the address before.

4. A P2SH address is the hash of an output script. In M-of-N the output script looks like "M ... M OP_CHECKMULTISIG". When a Tx spends funds from the address, nodes check that it contains the output script by checking the hash of it against the address and then check that the signatures match the public keys. When someone sends funds to a P2SH address, they are essentially saying "any script that hashes to this hash can redeem these funds." That script doesn't have to be M-of-N (though it may be non-standard if it isn't).