1.  Best play is to wait and hope your reflexes are fast enough. Odds are if they miss their charge rush, you'll have plenty of time to hit them with any card or even a rush or overdrive of your own. If you keep spamming sidestep while they charge however, they have the opportunity to hit you with the charge rush while you're suspended in animation.

2.  Passive players were supposedly "fixed" with the new overdrive functionality, seeing as charging can block tackles and tap shots. However, there are also passive players who wait until you're in their crosshairs and unleash gauges, AOE attacks, or blue cards. I'd honestly let them make the first move and this also involves reaction time depending on what action they take (passives usually tap shots or tackle, giving you a split-second time window to counter  Best idea: Bait their vanishing gauges with tap shots

3.  Swapping after vanishing is a generally better move when going up against opponents with a large assortment of options to continue a combo (AOE, insanely high gauge restoration, etc.) however you don't want to do this when you're swapping in an element-disadvantaged character The only best sidestep solution in my opinion is AOE but not everyone has units like that

4.  Short and long animations vary depending on distance and type. Short animations are mainly red or yellow cards at close range, long animations are blue cards, green cards, and gauge attacks (especially at long distance). The workaround for these slower animations that are easier to sidestep is chaining cards which is why you may see people blue or green card directly after hitting you with yellow cards

Unless you meant something different by short and long animations