I agree, I'd run the OEM spec oil. There's plenty of 0W-20 out there, and more on the way as well. Toyota's oil and filters are price competitive at the dealer.
You can run 5W-20. Technically, you're supposed to reduce the OCI from the likely recommended 10k miles back to 5k miles if you're running 5W-20. That's because the 5W-20 grade is available as a "conventional" oil, and I guess they don't want you running that to 10k miles.
You're changing the factory fill way early anyway, so I'll guess that you won't do 10k mile OCIs either. If you're going to do 5k mile OCIs anyway, you can run either grade (0W-20 or 5W-20).