Having finally returned home in the previous novel, TRPG Player’s eighth installment marks the start of the protagonist’s actual journey. All that previously happened was basically just prologue. That doesn’t mean you can skip ahead and start here though, as there are constant references to earlier events and characters.
I mentioned earlier that the third Mahou Sekai no Uketsukejou ni Naritai desu book basically felt like the end of the series and… I still feel that way after having forced my way through the fourth; it doesn’t add anything and happens to be terribly structured besides. Just stick with the first three and pretend this one doesn’t exist.