Speaking from a Property Managers point of view... You can always negotiate rent. Many times there is some leeway built into our owner agreements.
Depending on the area, we are getting multiple rental offers and the days on market is not long.
The downside to asking for a longer lease, it locks you in as well. If you have to move early and break your lease it will cost you. We just had that situation with a high end rental, they asked for an 18 month extension and broke the lease with one year left on it. They had to pay an additional 3 months rent.
If you have any questions, call me at 678-488-0183. Be glad to help