Reading the Odyssey is a must before attempting Joyce's novel ....
The Teaching Company has a course on Ulysses which has 18 lectures on the novel. These are 1/2 hour lectures for a total of 9 hours. The lectures are on dvd and an outline booklet comes with the lectures. The teacher is a prof with a Phd in literature. Google the Teaching Company and this course will be described and the cost given to receive the dvds and course outline. My library has quite a few of the courses given by the Teaching Company so I didn't have to pay for it. I highly recommend the Teaching Company and this course. You will learn more from this course than from any book you can get. But you still should read The Odyssey first. I'm from the old school and prefer the Alexander Pope translation in rhyme. If you want a faster read, try the T. E. Lawrence prose translation (Lawrence of Arabia). Once you have set through this course, you'll be able to read the novel easily. There are all kinds of allusions which Joyce makes, but these are personal things he knows about Dublin. There is a book on these, but it is thicker than the novel. When he (Joyce) makes an allusion to a butcher shop he used to go into, you don't have to know about this to read the book. I think he made these to confuse the pedagogues. You don't have to read any other book by Joyce before reading Ulysees.Good luck!
Must have been a different instructor ....
The lectures I saw made none of the statements to which you allude. They have a lot of different instructors in The Teaching Company, and I have run into some bad ones and some excellent ones. The lectures I watched on Ulysses helped me to get through the book, if not with ease, with a sense of accomplishment. It is a difficult book, and you have to want to read it. The instructor said, a friend of his who was a literature professor had a hard time with it and didn't finish the novel.