From closely observing a friend's TI fitted with a 13kg Suzuki 4 stroke, I would say that you do not need to counter-balance if the outboard is attached close to the hull, and, yes, the TI rudder is sufficient to effectively control the TI when under motor. Being able to steer using the outboard also adds a very handy redundancy...
Tony is referring to my endeavours to overcome troublesome rudder issues by adding a motor as a back up. I also sail from the rear of my TI which makes replacing rudder pins easier, however the ability of steering with the outboard can elevate the need.
Since seeing Tony I have made a stronger mount system as my previous reinforced aluminium tubing mount had to much flex. I have video of my prior system in action and will post it for you when able.
I try and balance the TI by carrying miscellaneous gear in the very front hatch. In the other hatches, where the front passenger sits, I carry my chart plotter/fish finder battery and in the hatch where I sit I have a small toolbox which is tethered and lies in the hull. In the bucket above that there are some bits and pieces like flash light, batteries, rudder pins etc. The rear hatch is empty.
The motor is a Suzuki 4 stroke which has a 1 litre top tank. I'm still running the motor in however I can confirm it appears fuel efficient. If I was going on a longer trip I have a special 1 litre back up fuel bottle which combined should give me a about a 20 klm cruising range.
The downside is finding the ideal height of the motor. Too high and the prop can be out of the water ( hasn't happened to me) and the throttle is at an uncomfortable angle. Too low and the outboard mount can be partly submerged. This all depends on speed and wave action. I think my new mount is better but not perfect.
I rarely use the motor however coming back against wind and tide makes things easier especially when you have a passenger that is feeling a bit uncomfortable. There is the additional benefit of having a back up and the possibility of venturing further.
hope this helps