Only to book four? Then how do you explain the eight volumes sitting on my shelf?
ADV was supposed to release the ninth on 2/28, but it looks like it's been postponed. I'm confident that it will be released though. I think the ninth volume might be the last. The first manga covers about the same material in the novels as the first TV series did, some of the side stories that went into Fumoffu, and some side stories that haven't been animated. There appears to be a new FMP manga called FMP Sigma that will cover about the same material as TSR. Then, of course, there's Overload which doesn't use any of the previous incarnations of FMP as source material, but is an original series targeted toward a younger demographic.