By all means, read 19th-century English if you are interested in literature, and in the history and culture of English-speaking countries. You may struggle, as even some native speakers have trouble with some vocabulary and phrasings that are no longer current . But in terms of your general education, this can be a worthwhile experience. However, do bear in mind that reading texts that are nearly two hundred years old is unlikely to improve your English. In fact, it could even cause problems, as you are likely to learn outdated and even archaic usages. Very little of the English used in the literature of the 19th century is appropriate for everyday use today. If you want to improve your English through reading, you need to focus on literature of the mid-20th century or later.

I would agree with other answers that have been given. There is certainly the danger of learning archaic words and structures that are rarely used. That said, it will help you see the range of English grammar. 19th-Century literature tends to have very complex sentences. So if you want to a grammar challenge, it could be a good way to get used to complex sentence types. You may also be able to find some of those books redone in more modern English if you want to compare them. Those would not be free however. If you're looking for free reading material, you might try looking for fan fiction sites online. These tends to have stories that are free and you might find something that interests you. You could also look on Amazon which has search options for ebooks that cost $1 or so. eBookhounds is a great place for getting news about cheep English ebooks. I hope that helps.

You can read them out of interest or leisure, and you may find some cases where it may be useful (essay writing for example). But generally speaking, yes.. a lot of words are archaic, ancient even. Not recommended for daily speech. You are better off reading anything after the 1980s.

Many Western classics belong to that time period, so I would say that they are a good challenge for an upper intermediate, but I would get a modern edition with notes to explain outdated concepts and old-timey stuff like types of carriages, and those aren't usually readily available for free. The title is usually something like, "The annotated Pride and prejudice".

Because the books are out of copyright you are more likely to find dual language books on line.