1. 6C and 2C aren't good anti-airs. 623B is punishable on instant block and a psychic one can lead you wide open. 623C and 623D aren't exactly best used as anti-airs. So 623A and j.A at close range might be your safest options. If you use C dp while getting crossed up by j.B, they will probably land in time to block. Depending on their location in the air, you can backdash to avoid this move and follow up.
2. Just IB 5D and wait a bit to see if they do something else. If they don't, free combo. If they do, it has to be a punishable dash cancel or a special move so IB high since his moves are easily figured out. Watch out for RC. Also, don't DP. You won't rewarded that much and having the Ragna burn heat is a much better option.
3. His 5A does suck, but if you're crouching, he may try to whiff throw. 2A that shit if you see it. If your reaction is poor...2A. 5B is too good, but just respect it and find holes in his soon to come pressure.