I've done some research and you're right: they were both dissertations. And he wrote them both at the same time. Apparently that's how the French Philosophy Phd thing was (or is)structured: between a "thèse principale" (main dissertation) and a "thèse secondaire." DR was the thèse principale (I also remember now an article by Foucault about DR when it came out, presenting it as one of the most important Philosophy books of the time -or the 20th century- or ever, I can't recall...but it seems to be presented as pretty BIG)

I've never really had the feeling that you had to read the previous book to grasp all the references in the book of his you were reading (except when they follow as in "Cinema I and II and Capitalism and Schizophrenia for example) but then it doesn't necessarily bother me not to understand everything. Actually, I find that one of the great pleasures of reading D is to figure out what you can, while the imagination is busy trying to fill in all the gaps. it's very much like reading poetry sometimes. He once described his classes as a place where people (all sorts of people : artists, sociologists, students, etc...) came and kinda slept, then suddenly, something somehow concerned someone and that person would wake up for a while, then someone else would wake up, etc. i find that reading his stuff is a bit like that: i don't feel concerned by it all in the same way...

He's obssessed with certain figures, but they're probably also like poetic figures in the sense that they have a polysemic potential. the dice image for instance is evocative on its own, it refers to the Nietszche thing, but also to the Mallarmé poem (which i find outrageously difficult) "Jamais un coup de dès n'abolira le hasard" ("a throw of dice will never abolish chance") etc...

i don't really have the feeling that his work is to be understood as an absolutely coherent whole (and he greatly admired thinkers who suddenly altered their thought drastically) But you do get to a stage where the more you read and the more consistent some of the stuff is (in that sense I also enjoyed Badiou's reading of Deleuze which casts a really unexpected glance on the whole body of works).

And i've found that his oral expression was sometimes much clearer as it wasn't as dense. The've started transcribing some of his classes on a website (www.webdeleuze.com) but i don't know how far they got with the English translations. I was once advised to read a class he gave on the introductory chapter to Bergson's "Matière et Mémoire" which made a lot of things clearer (that chapter appeared as a crucial reference for all his work but was only really developed in "Cinema." so sometimes the answer comes later also...)

I really get the impression that in order to grasp stuff such as DR ands the Spinoza, I would have to read and grasp other things. I get the impression the most competent people on the matter wouldn't necesarily be the Deleuze specialists, but people with a sound academic philsophical background, people who really know their Kant and Hume and Spinoza and who can figure out where he really stands in his "own" field. (people who can also grasp the political, aesthetic, etc consequences nowadays of being a spinozist for example would also be nice, but that still entails the same kind of background)

Lacking that background, I still feel like a guy waiting to wake up at the back of his class (at least in the case of some of his books, among which those you're planning to read)