What a difficult decision! I wouldn't say it's impossible to do Lit 3/4 without 1/2, but I think it would definitely be a challenge as the two subjects are quite different.
If you decide to go with the change, I suggest being aware of the following:
reading load. The reading requirement of Lit is more than English. You'll have to read at least one more text as well as multiple articles in order to be really prepared for it
the depth of knowledge required. As you mentioned, English's focus is on breadth (which you sound frustrated by), while Lit's focus is more on depth. This means you'll need to be prepared to really dive into the text in your analysis - focussing on single words, motifs, etc
the jump in vocabulary/metalanguage required. In Lit there is a priority on the accuracy of vocabulary, which means that you'll need to wield (accurately!) a big range of vocabulary in order to fulfil the requirement of sophisticated language and analysis
In regards to your question about homework...how long is a piece of string? 😉 But in seriousness, many top lit students will write multiple essays in preparation for each SAC, so that equates to roughly one essay a fortnight throughout the year. This is a VERY rough estimate so please take that with a grain of salt!
My other advice for VSV, which you didn't ask for but I'll give anyway, is that it can be a little lonely, particularly if you're the kind of person who enjoys talking about texts with your classmates and in the classroom. Some students struggle with motivation without the regular in-person classroom environment, and it's a common struggle to organise your time efficiently when your in-person class work seems more pressing. That said, it's not a reason to abandon the choice - I just think it's helpful to walk into it with your eyes wide open and ready to take on the challenges.
Good luck with whatever you end up choosing!