이번 주말에 저는 많이은 것들을 하지 않았습니다.

많이 here is weird because it expresses a degree, except you never specify *what* you're doing to a large extent/degree/"a lot."
Alternatively, you can also say something like 이번 주말에 저는 한 게 별로/많이 없습니다. In that case, you'd just be saying that the things you did do weren't a lot.

저는 또한 많은 친구들을 만났습니다.

While this is perfectly correct and valid, note that using 또한 like this is extremely formal. That does fit in okay because you are using 하십시오체 (formal polite speech pattern, e.g. -습니다) but I think you could still turn down the formality a bit depending on your desired audience.
One thing you can do is just replace 또한 with 또:
저는 또 많은 친구들을 만났습니다.
Another thing you can do is to replace 많은 친구들을 with 친구들도 많이, which IMO improves the flow a bit:
저는 또 친구들도 많이 만났습니다.

If you'd like any clarification on this correction, please feel free to ask in the comments!

지난밤 나저는 새벽 4시까지 TV를 보았습니다.

Politeness mismatch

하지만, 이번 주말에는 책을 읽을 계획입니다.

It's unnatural semantically unless you include that 는 there to indicate that you're forming a contrast with the previous sentence.