If I use most of the references from a thesis but not the exact same sentences, is it plagiarism?

Working from a bibliography in another paper is not plagiarism. It's actually a good research technique. As you read those papers, check their bibliographies, too, and so on. Pretty soon you will have thorough coverage of the subject.

Do note that you cannot just plop those 50-60 or so references into your own bibliography but do nothing else, nor paraphrase what someone else has said about them, but without reading them. That's called reference padding and is academic misconduct. You have to actually read the papers. When you do that, you may find that some of them don't fit your needs as well as you may have at first thought. You will also find it easy to write your own thoughts about those papers, and so will not have to worry about paraphrasing another author.

Using references that someone else used is not plagiarism.

That said, if you made significant use of the thesis text itself (not just its bibliography) in understanding what the references were and how they might be relevant, it's worth citing the thesis as a source for more information. For instance, if you got some ideas by looking at a chapter in the thesis titled "Cake-baking", reading its summary of different cake-baking techniques, and then looking up the references in the bibliography to get more detail, then you didn't just use the bibliography, you used the textual explication/summary of the cited material. It's common in articles to see a discussion of previous research with various citations, and then something like "See Jones (2000) for an overview of relevant research in this area."

No. Taking someone else's bibliography, reading those papers, and writing some words of your own about those papers is not plagiarism.

Don't restrict yourself to just those papers, though. In all likelihood, the thesis writer won't have cited every resource that is useful or relevant to your work. If there has been a recent review published on the topic, that's usually the best place to start your own literature survey.