F-Air at lower percents when it's difficult for them to escape the second hit, u-air if you can't seem to hit with F-Air, B-Air at high percents for KO/edgeguard.
you have a good sense of ZSS's speed, but you let it run wild. She's an amazingly fast character compared to most, and sometimes that makes us feel like we're unpunishable when we come in with our moves, but our approaches can get ***** pretty hard. Make sure to space properly, be careful with your dash attack approaches.
As for moveset use, I would suggest using more u-airs and cutting back on the b-airs. b-airs are great late in the stock when you can get KOs with them, before then, you'll just be decaying your best kill move; the damage is mediocre (only 3% more than u-air) and can't be followed up with anything. Of course, cut back on d-air and f-smash... horrible moves. I also noticed you used side-b even when your opponent was fairly close to you, you should probably stick to tilts or d-smash for situations like this, the deadzone of the side-b is unforgiving.
As for edgeguarding, don't be afraid to jump out after your opponent. In the Dedede match you jumped out after him and landed a b-air in his face for the early KO (early on dedede anyways). RAR'ing off the stage and b-airing your opponent is a great way to pick up some early kills. If the char doesn't have good recovery, it basically insures an easy edgehog, if they're close to the wall, it might just outright kill them immediately.
As for recovering, be careful dilly-dallying off the edge. If you can tether, tether immediately, don't let your opponent have time to think of ways to edgeguard you. I noticed once in the Sheik match you were foolin' around off the edge attacking no one and got shamelessly edge hogged for it, I consider that a lesson learned. d:
postnote on recovering: the best way to cancel momentum vertically is to hold down while performing a u-air (fast falled u-air), the best way to cancel momentum horizontally is an airdodge and then down-b towards the stage.
overall, good ZSS. I really like your use of U-Smash, I've never personally been able to connect consistently with it.
keep it up!