Some General things you want to know about Weiss are that
1. Although 5C is good, don't autopilot into it with pressure strings. if the opponent 4/6GC's it you'll eat a combo
2. Always try to be equipped. When you're equipped, 2A, j.A, and j.C become excellent tools.
3. Use 5B to jump cancel and bait out those guard cancels. especially if they're happy to 4/6GC if they expect a 5C
Against Scharl you MUST be patient. Remember that you can throw out mulitlayer (236236E) between 5C and Vine.
Also when playing against a character like Maori,Nazuna, or Yoriko I recommend going with Halo.
Also if you're going to transition from Time to Flower or something else (Which I recommend, and kudos for you for deciding to do that.) I strongly recommend that you learn some EFC equip combos. Here's an easy one to learn.
5A/2A 5B 5C 4B 623C EFC (step) 5B 4B 5B jc. J.C j.B j.C j.E J.C land 4B 2C 22A
From there you can forcestand them with 2A to start mixup
Flower's a really solid pick with Weiss (In my opinion its the best pick for her.) but I also recommend trying out Love, Halo, Plant, Thunder, and Evil.
Hope my post covered some things for you, if you ever have more questions, feel free to ask. Hope this helps you out