1. This usually means you reacted to slow in your combos or missed the timing and your opponent failed to tech out of it. 4. IIRC this isn't possible on the ground and IAD is usually used to cross-up/ mix-up the opponent however, some characters can IAD in air combos to continue combos but I forgot which ones. 5. RCs are useful in combos in the way you stated, but I usually see them as a way for people to save themselves or as a form of mix-up, but the more common way is for them to use FRCs to put the opponent in a stun-lock state or create hard to react situations. For example, sol using his gunflame and FRCing it to create pressure while sol finds a way to break your defense.