If you want to rent an apartment through a real state agent, to try to pay less to them is an awful strategy.
Be careful, there is a common fraud regarding reservas. If they ask for too much money, like they did, for reserva, they don t care about renting the apartment later because they already have your money.
When you ask the money back, they start a criminal prosecution denouncing threats.
So, if you made a reserva then you have to pay the real state agency the 2 months they asked you. Otherwise, you shouldn´t made it.
Nowadays it is normal, but still abusive, that they ask for 2 months of commission.
You don´t need to have a clause regarding finishing before the 2 years the contract because it is on the law. The renting law is a "public order" law. It means that any clause against it, it´s considered not written. It also means that even a clause is not in the contract, it is enforceable if it is in the law.
You can leave any time just notifying the owner with some time in advance by carta documento. If you leave before the 6 months, you have to pay until the 6th month even you are not there. If you leave later, you loose the deposit. That´s why you shouldn´t give them more than 1 month deposit.
Regards