Is this a DK weight yarn?

Hello, Scheepjes Mandala Yarn is not DK weight. It is #1 - Super fine/Sock and is more like a thick string. When I received it I had not known that it was so thin and since I had never worked with anything that thin before, I almost returned it. But I wanted to make the mandala, so I gave it a try and was so glad I did. It crochets beautifully and I never had a problem with splitting. The mandala vest I made for a gift turned out lovely. I want to make another and enter it in the state or county fair this coming summer. One small looking cake is nearly 1100 yards, so you know it is super thin. Good luck.

What crochet hook do you use for this yarn?

For the project I'm currently working on right now, I'm using the 2.5mm (C) in US. It is fine yarn, so you'll probably want a smaller hook.

Does this start in the center or the outside?

Outside, but you could re wrap it to start in center! Love this yarn!!

What whirlette matches the pistachi so nice one?

I have not found a good whirlette to match pistachio so nice. I ended up purchasing another whirl to finish my project. You could use a contrasting color (chewy for the outside, or frosted for the inside) but it will definitely look different.