Sludge isn't really an issue on the 3.0s or the 3.3s as long as it has had semi-regular oil changes. The sludge prone ones were the early 1mz-fe from 98-2001; my understanding is that the later ones have some revisions.
These are relatively reliable engines but since it's a transverse V6 in a FWD engine, labor time to do any work will be high. You can expect to re-seal the valve cover gaskets and the water inlet (which is in the valley area below the lower intake) at some point, and book time on those are about 5-6 hours. If you ever have to reseal the water inlet, I would also replace the wiring harness for the knock sensors since they can get crispy.
Plugs can be done without pulling the intake plenum if you have good hand-eye coordination and only remove the t-body, but I prefer to remove the intake to do them.
If you do not have a lot of experience with working on cars, these can be a little intimidating to work on since A LOT of stuff has to come off to remove the manifolds.
For the transmission, I do a 12-quart flush with T-IV (purchased from the dealer) every 30k. This fluid is very inexpensive from the dealer (about $50 for a 12-qt case) and the short interval keeps the transmission healthy.
Timing Belts are due every 90k, I would get the Aisin Kit from RockAuto since it includes everything you need and the parts are very high quality compared to Gates or Dayco. For drive belts I would get Bando from the same source.
Regardless, I would not hesitate to buy one.