First time getting Botox - where is good? (Jaw/Forehead)

I'm planning to get Botox for the first time.

**Areas of Concern**
- Square jaw (teeth grinding habit)
- Forehead wrinkles

**Questions**
1. Can I get both areas done at once?
2. What's the appropriate dosage?
3. Any recommended clinics in Gangnam?
4. Is there a difference between Botox brands?

Please let me know the price range too!