Storvald's triggered ability will overwrite any previous effects that set the creature's power and toughness to specific numbers. Effects that otherwise modify that creature's power and toughness will still apply no matter when they took effect. The same is true for +1/+1 counters.

If you choose both modes, the effects will happen in the listed order.

You can choose the same creature as the target for both modes if you wanted to—I don't know . . . give it a small taste of phenomenal cosmic power before shrinking it so it could live in an itty-bitty living space?

If a player casts a spell that targets multiple permanents their opponent controls with ward, each of those ward abilities will trigger. If that player doesn't pay for all of them, the spell will be countered.