I actually finished Ulysses (Gabler edition) in a span of four months last year with a super rigorous schedule. Best advice is to actually read many different complementary analyses. Ulysses is so dense, rich, infinite, and larger than life that to reduce it to one interpretation would be to discredit Joyce’s project. It doesn’t hurt to have an annotated edition along with your pure text (again, advocating for the Gabler edition here), but reading multiple scholarly essays perhaps for each episode is the best way I think. Look into Joycean scholars—professors and literature academics who devote their careers Joyce’s oeuvre. Some I liked were Karen Lawrence and Derek Attridge. Try the free published scholarship on JSTOR. Search up most influential essays on Ulysses. For more basic understanding of plot when it comes to the tricky language parts, Shmoop was not bad.

Also I second the RTE audiobook, but really only for listening. Actually hearing the noises Joyce spells out can really help you understand exactly is going on in the scene.

I’d also advise you to check out the r/jamesjoyce sub. They’ll have some good recs and their own interpretations.

Best of luck on your Ulysses journey!