A lot of the books and posts I've found seem to be dated. Are they still good enough to get started with or are there better options?
If it's the first, you should look at HuggingFace, which package transfer learning in a very accessible way to use. But I'd say that's probably too a big leap from no experience at all to that.
I wrote a detailed article on how to get up to speed with NLP - tracing the path I have gone through. My main thing was getting quickly to the point where I could actually use this stuff:
https://towardsdatascience.com/learn-nlp-the-practical-way-b...
For theory on NLP with deeplearning you can follow Stanford course by Christopher Manning.
http://web.stanford.edu/class/cs224n/index.html#coursework
it will give you a good understanding of how deeplearning is used in a certain area of NLP. But remember deeplearning is one of the techniques for solving NLP problems if you are more interested in Understanding NLP then I would recommend the following book.
https://web.stanford.edu/~jurafsky/slp3/ed3book.pdf
Although, Stanford course should give you a great high-level understanding of how GPT models work but if you really need to go under the hood then I would suggest after finishing this course you should learn Unsupervised Learning in DeepLearning.