The sky is the limit. I'm no expert, for sure, but I'm not afraid to work on my own vehicles. I've done all the maintenance on my E30, and it's pretty straight forward.
I have 3 sources for reference
1. Haynes Manual
2. Bentley Manual
3. BMW Enthusiast's Companion
By far, I would say that the Bentley is the best. Of course, I try and use the internet for stuff as well.
You're going to need a metric socket set for sure. All sizes. (You're going to use 10, 13, 17, 19mm a lot) I have combination wrenches, screwdrivers, and allen (and torx) wrenches. I have some other assorted tools, but you're basically going to have to start with a good set of each of the above. Also, before you go ahead and start on that timing belt, ensure you have something that is thin and large enough to get the fan and clutch off. I'm pretty sure it's a 32 mm nut, and it only needs to be broken loose, it will hand loosen from then on, but if you don't have something to get that off, your maintenance will come to a screeching halt.
Hope this helps.
oh, and about your transmission, did you check your fluid? (I'm sure you did)
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