I have a hobby interest in linguistics, but have no intention of studying it at a University. 
What are some good ways to build a solid foundation in that field?
If you have a hobby interest in linguistics and want to build a solid foundation in the field without enrolling in a formal university program, here are some tips:

Start with introductory books: There are plenty of introductory books on linguistics that are accessible to beginners. Some of the popular ones include Language Files by Ohio State University and Linguistics: An Introduction by Andrew Radford et al.

Watch online lectures: Many universities offer online courses on linguistics, which can be a great way to learn from experts in the field. Websites like Coursera and edX offer a range of linguistics courses that are taught by professors from top universities around the world.

Listen to linguistics podcasts: There are several podcasts dedicated to linguistics, which can be an excellent way to learn about the latest research and trends in the field. Some popular linguistics podcasts include Lexicon Valley and The Allusionist.

Join online communities: There are many online communities of linguistics enthusiasts that you can join to discuss the latest research, ask questions, and learn from others. Reddit has a dedicated linguistics subreddit, and there are also several linguistics groups on Facebook and LinkedIn.

Attend conferences and workshops: Linguistics conferences and workshops are a great way to meet other linguistics enthusiasts and learn about the latest research in the field. Many conferences and workshops offer student rates, so you can attend without breaking the bank.

Learn a new language: Learning a new language is an excellent way to develop a deeper understanding of linguistics. As you learn a new language, you'll begin to notice patterns and structures that are common across different languages, which can help you develop a better understanding of the field.

By following these tips, you can build a solid foundation in linguistics and develop a deeper understanding of the field.
What branches of linguistics are there?
Linguistics has many branches that focus on different aspects of language and its use. Some of the main branches are:

Phonetics: The study of the physical properties and production of speech sounds and equivalent gestures in sign languages.
Phonology: The study of the abstract system and patterns of sounds in a particular language.
Morphology: The study of the formation and structure of words, including their smallest meaningful units (morphemes).
Syntax: The study of the rules and principles that govern how words are combined to form sentences.
Semantics: The study of the meaning of words, phrases and sentences, including how they relate to each other and to reality.
Pragmatics: The study of how language is used in different contexts and situations, taking into account factors like speaker’s intention, listener’s inference, social norms and cultural background.
There are also many interdisciplinary branches that apply linguistic methods and theories to other fields or domains, such as:

Historical linguistics: The study of how languages change over time and how they are related to each other.
Applied linguistics: The study of how language is used for practical purposes, such as teaching, learning, translation, communication or policy-making.
Sociolinguistics: The study of how language varies according to social factors like region, class, gender or ethnicity.
Computational linguistics: The study of how language can be processed by computers or artificial intelligence systems for tasks like speech recognition, natural language understanding or machine translation.
Psycholinguistics: The study of how language is acquired, processed and produced by the human mind and brain.
Comparative linguistics: The study of how languages differ or resemble each other in terms of their structures, features or functions.
Stylistics: The study of how language is used for artistic or rhetorical effects in different genres or texts.
These are some examples but not an exhaustive list. Linguistics is a vast and diverse field that covers many aspects of human communication
Ugh your answer is way too long! I'm not an AI like you, please answer the question in a more synthetic format.