Flight booked, but no seats confirmed?

Hello,
I have an Air China flight booked from Seoul to Beijing. I'll land on Sunday at 10am.
My flight out is at Tuesday at 3AM on Ukranian Air.
My 2 questions are: I have the e-ticket and it's all booked, but not my seat assignments. Is that okay?
Also, should I book a hotel ahead of time? I'll most likely book for just 1 (Monday) night and get to the airport that night. That should work right?
Thanks,
Brian