1) does sprinting make inf harder to hit because faster, or the difference in received accuracy is only between moving and standing?
2) do units which just ended a sprint, so while they have red aura and move slower, get some other kinds of debuffs? Increased reload time or suppression for example.
I can say about number 2: yes. They received accuracy is higher, also their reload speed and accuracy is lowered. That is why I never use sprint ever. It's very dangerous ability that can do more harm to you than it can help.
At Vet level 3 the bonuses are the same but the sprinting phase lasts 15 seconds instead of 10.
Then there is the "Fire up" ability (some AB units have this) - this works a little different it removes any suppression the squad has and the squad becomes impossible to suppress while the ability lasts (15 seconds) - during this time the infantry is also don't return fire while moving, also have lowered sight range by 10, have lowered accuracy by 15% but are also easier to hit by 15%. After the ability ends they have same penalties as during sprint.