2) You cant choose the hatcher, it chooses you. You can request some parameters, such as trust level, min fee, but your broadcast goes system wide.
EDIT: Your next transaction is sent to a different hatcher, you can not send a transaction to the same hatcher twice in a row, and the network can see this as the hatcher signs the transaction.
I'm basing this on the above. If clients have a configuration for "trust level", then hatchers with higher trust are going to be favored by clients over hatchers with lower trust, and hatchers with no trust at all will probably have to wait until there are no other hatchers available to service transactions.