The first thing that comes to my mind is the surface of the brake rotors! sometimes, the brake rotors get badly scratched or someone puts water on them when they are too hot so they change their shape a little bit and this gives vibration to the steering wheel... while this is the most probable cause, out of balance wheels can also cause the same.u might just have to get ur rims balanced but that wont eliminate the "slip" thing... first, let me know whats the tire size? if its anything below 185 then its not enough for the car and the tires do not have enough tread to grip on the road...
but it can be something wrong with the suspension too, due to which the tires might not be properly sitting on the road.
To start, i'd say get ur rims balanced (if there is vibration in steering wheel without braking at high speeds) if the problem stays, get the brake rotors off and get them faced/polished by some "kharaadiya" it will cost around 300rs for 2 rotors plus 200rs for labour, taking off and fitting the rotors... by now, much of the problem should be gone.. if it stays, get ur suspension checked.
As for brake pads, its ur choice, a good road side mechanic can fit pads as good as Honda guys would...