You are never obligated to sign a contract. You already have a lease agreement in place, which will be enforceable for the agreed-upon duration. The lease can be changed if both parties agree to it, but one party cannot unilaterally demand that other agree to any changes to the contract - a landlord can't, for example, change your lease agreement to increase ...
If you turn in an N9 form and move before the six month period is over, the landlord is supposed to make his best effort to rent the property to someone else.
If no one else rents it, then you should compensate the landlord for whatever the losses were.
That means, if it takes two months to find someone to rent the apartment, that you should help cover ...
No, you can not break the lease early without an agreement or their would be no reason to have a lease. You would just pay by the month.
If you aren't sure you want to live there for the whole term of the lease you should probably keep looking.
You are correct that the landlord can't evict you with less than two months notice. However note that you might want to avoid enforcing that because a good reference from your existing landlord is likely to be very helpful when looking for other property.
According to this page on the government website:
You may be able to apply to a tribunal to reclaim ...