I tried this, and it has been saying "pending evaluation for over an hour. Maybe because this is my first time setting up an EC2 instance?
The price for the spot instances is rising. Perhaps you did not bid high enough?
No if your price is too low you get "price too low" message. Something else is wrong with his configuration.
a way to have a full node start mining automatically upon launch?
create a script start.sh in your home directory:
./bitmonerod --start-mining [addr] --mining-threads [threads]
Use the command crontab -e to edit your crontab file. put the following line in there:
@reboot sh start.sh
Reboot to test. If it works, make an image of it, use that image to start more instances.
Since you are coding in the number of threads you probably want a different image for each instance type
EDIT: Also be sure to open port 18080 (incoming tcp). You can do that when you launch the instance or you can do it when already started by modifying the security group for it.