Are there any mistakes in the following text?

"I want to express my gratitude to all those, from whose hard work and determination I've learned so much and will continue to learn in the future (some of whom I haven't had the pleasure to talk to personally but have pursued their work over the years)."

1. For some reason, I don't feel good about "those" being used like that by itself (especially because there was no earlier mention of those people. We don't know who "those" are yet. That's just the start of the sentence. The names are supposed to come later).

2. I'm not sure if a comma should be used after "those" since the following adjective clause is essential.

3. Using "their" in that adjective clause sounds clunky to me. But then again, some subtleties can only be discerned by a native ear. I may be wrong.

I was wondering how native speakers of English would feel about my questions and generally the whole text.

P.S. I believe this in not a proofreading request. I have certain questions in mind regarding determiners (not sure if "those" is a determiner or a pronoun in that sentence, I would appreciate a clarification about that too) and adjective clauses. Writing a paragraph was my way of providing a clear context. I don't know how I could've chosen a better title or formed my question in a better way.

Thanks a lot

As a native speaker, I would be happy to help you with this proofreading process.

I agree with your assessment about the removal of the comma after 'those'. Regarding the use of the word 'those' itself, there is no reason to not use it as, in this sense, it kind of means to say 'those people' and the word 'people' is omitted but understood. (Think about the phrase 'Give to those in need'; the word 'people' is implied.) Finally, your use of the word 'their' is perfectly fine.

If this is being written for a formal event where it will be spoken, the language is perfectly fine; if it's a formal bit of writing, that comma is ungrammatical. If this is being written for a semi-formal or an informal event, the language comes off as too formal — almost pretentious. Either way, I don't see anything wrong with it outright with the exception, of course, of that potential for sounding pretentious in an informal setting.