Unfortunately, when it comes to word limits everyone will tell you 'it depends'...but they're right. Everyone's project is different. I was told 8,000-10,000 per chapter and that has worked as a good guide for me. A lot of academics I've spoken to about this say anything beyond 10,000 words per section is too long (and you should really be thinking that you're trying to compress too much into one section). You'll probably find your first draft is much longer than that, but when you're forced to narrow it down you start to focus on what's important. If it helps, my lit review is going to be around the 10,000 word mark (although it started off more like 20,000!).