Yes. The curve, spin, timing, particle counts, colours and physics are read from the Minecraft 26.3 client, and it uses your pack's own totem, particles and sound.
No. A pack you add is read in your browser and stays on your computer.
Java packs of any age, 1.8 PvP packs included, and Bedrock packs. Anything a pack doesn't change shows as the game's own, so you can see exactly what it does.