I have an 08 and I love it too. Check out the 120 section on IH8MUD for lots of great builds.
GXs are North America's rebadged version of the Land Cruiser Prado 120. They share a frame/suspension/driveline components with the US 4Runner and FJ Cruiser, but from the frame up they are completely different, so the aftermarket for bumpers, sliders, roof racks, and anything interior is limited to a handful of fab shops that make GX stuff or vendors who import Prado stuff from Europe, Australia, and the Middle East. However, the aftermarket is growing now that more people are becoming aware of their off road prowess.
The engine and transmission are known to be pretty bulletproof, but the 470s are all 10+ years old at this point, so there’s lots of small maintenance items that can add up fast. Fluids, bushings, ball joints, belts, suspension, etc.
Common problem items include cracked exhaust manifolds ($$$$), rear air suspension pump/airbags failing, front brake calipers seizing (it’s common to swap them for GX460 calipers - they use the same pads), rattling sunroof, rear driveshaft thump (TSB), cracked dashboard (was a recall, but it’s over), driveline vibration (TSB).
-03 is the only year with a transmission dipstick (I think) - the rest of the years are “sealed”
-05+ has a VVTI motor with like 30 more HP
-07+ the navigation was refreshed
-08/09 have clear turn signals, chrome accents, and dark brown wood interior accents (vs light wood)
-“Sport” models have KDSS standard and smoked headlights - you can easily spot them by their black wood accents in the interior
-KDSS was also an option, but not common outside of the Sport
-Some people prefer non-navigation models because it’s easier to replace the radio - it’s worth noting that there aren’t many options to replace the factory navigation units because the HVAC controls are integrated (I think there’s one option and it’s a Tesla style unit)
I’m sure there’s a lot I’m missing, but I hope that helps