Brother to your first concern regarding vibration. Apparently there could be 3 main reasons for this issue. (a) The gearbox (b) Axles (c) The Engine Mountings.
The safe limit of AT oil change is around 45K kms. Change the AT Oil and see if you feel a difference as car is close to 30K kms already.
Have the mountings visually inspected. The rubber core on any of the mounting could have started to fail slightly. Bear in mind that civics have been prone to this defect earlier and Honda tried to rectify it as one of the mountings on reborn would fail as early as 25K.
The axles could be another cause but consider them at the very last after the first two options have been ruled out. Do Have the outer boots checked on each side and jack up the car to check the inner ones for any leaks. Don't concern yourself with changing the axles just yet. If your axles are the cause of vibration for now, then wait till your car gets more mileage, this vibration should amplify with time. The vibration will get to a point where the whole chassis of the car will vibrate and shake at certain speed (it will drive smooth either above or below that speed). That is when axles will need to be replaced.
For the second concern about your car pick I think it needs a good tuning and a good mix of Super & Hi-Octane (I keep 50-50 all the time) & should be good to go.
