What do you hope to get out of the books? General PS knowledge, or do you have something specific in mind? Understanding layers is pretty fundamental, and will be a required foundation for truly getting the idea of masks and channels. That being said, if you dive into masking and ChOps, you’ll probably get the hang of layers pretty quickly.
Is there any chance you can look at both in a store before buying?
As for the color space, PS uses Lab natively, and ‘translates’ to all others. After you’ve gotten through the other two books, I highly recommend Dan Margulis’ ‘Photoshop LAB Color’. There’s a lot of technical work in it, but if you truly want to understand using color in PS, I mean at a level where it becomes intuitive, get that title.
So, my recommendation, without more detail about your needs or experience, would be to get Deke’s book (Masking), then Photoshop LAB Color. If you are truly a beginner, start with Richard’s Layers book.