Ok, everyone, correct me if I get anything wrong here...
There is a company called "Professional Publications, Inc." that has a
website. That website has some forums set up for people to talk about taking and studying for the PE exams. They way I understand it, the forums are heavily censored so that if you post negative comments about the products that that company sells, or their review courses, those comments get removed. Since people tend to bitch about stuff when they get stressed (like when the exams are looming), a lot of posts get removed. Also, any "shoot the breeze" and "off topic" posts tend to get deleted by the moderators.
So, a few years (I think) ago, a couple of the regulars from that board got sick of having their negative (but informative) posts removed and decided to create their own forum. I believe that at least one of them actually got banned from the other forum for some reason. As a joke, any time someone types in the letters p-p-i without the dashes, this forum replaces those letters with "the other board" in quotes. That said, some people find the practice problems and exams that can be purchased on that site to be helpful. Others don't.
By the way, I'm not mech, so I have no clue what books you should buy. Sorry.
In general, I would say that since you have a lot of time, work with what you have for now. I'd set up a schedule that would allow you to be through all of the MERM practice problems by the time you're 8-10 weeks out from the exam. At that point, take a practice exam or two (don't even look at the practice exams before that time). That will help you figure out where you need extra practice and you can purchase additional materials at that time, if needed.
Btw, the NCEES practice exam is published by NCEES (you can buy it directly from them). For Civil, it has 20 breadth (morning) problems and 20 depth (afternoon) problems for EACH specialty. Some people say that the NCEES practice exams are the closest (in terms of difficulty and type of problems) to the real thing, the other practice exams that are out there are generally more difficult.
Good luck.