!)Personally I think the hardest matchups for chin are: Daimon, King, Benimaru, EX Kyo, Ex Iori.
Daimon and King are hard because of their good pokes, especially st.B which hits low and have good range. Chin gets out poked easily. In close range, Daimon's grabs beats many of Chin's options. Against good King players who know the range of Chin's barrel rolls, it's hard for Chin to get in.
Benimaru is tough because of his jump arc. He can basically vertical/jump back D all day and wait for Chin to make a mistake.
EX Kyo and Ex Iori (and to a lesser extent the regular versions) both rush down Chin very well. Chin has to be very on point and make good guesses with his options.
2) Chin's counter is 1-frame. It is a good reversal only if your opponent is predictable since it only counters either high or low (ex version counters both but has very little active frames).
3) Press B+D to cancel kick stance is the fasting way. Your other options are cancelling it into another special (counter, Ex back fist, Ex roll, etc).