Soldering is not that hard, if you understand what you are trying to do. It is supposed to be quick, 120W soldering iron won't be a problem if the soldering will be done quickly.
But since you are totally new to soldering, it generally takes longer to solder a piece on your initial runs, and the heat of soldering iron may cause damage to plastic parts nearby in this time, especially if the soldering iron is too powerful.
25-40W is a more reasonable power range for this type of work. 120W is too much.
By "bending the negative motor connector" do you mean the male connector on your motor or the female connector on the end of the wire that goes to the motor?
Last edited by ccyg8774; April 8th, 2015 at 21:40..