French language Q&A Forum

I won't again write "jeudi suivant" in quiz answers but I hear it a lot when making plans, so I'm putting this here :-)

https://forum.wordreference.com/threads/jour-de-la-semaine-prochain-suivant-qui-vient-de-la-semaine-prochaine-dapr%C3%A8s-en-huit.377114/

Shouldn't this be:

Marie "EN" a déjà tous achetés.  

Since the article here is "des" and not "les"... We just know there are "some" presents to buy, not any specific ones.

I am looking for when you would use de plus en plus and when to use de plus en plus de. I can't seem to find an answer, if anyone knows that would be great.

Why "Je vais chez le boucher" and not "Je vais au boucher" when for going to boulangerie and marché, the answers are " je vais à la boulangerie" and "je peux aller au marché"? Are there certain places we need to use "chez" instead of  "à"?