Hate to break the news to ya, but it's not too hard; I set up such a thing in an afternoon to generate traffic to load test an app I am developing. The commandline tools are pretty well documented for this standard workflow.
I do the first part manually, using the web console: 1)
1) launch an instance, install your code on it. Bonus points: write a script to parse the UserData so you can tell it where to pull the source data from (I keep such things in S3 if needed)
2) use that instance to create an AMI.
3) Use the run-ec2-instances command line tool to launch some instances of your AMI
4) Either configure the instance to auto-run your tools on boot, or use ssh to remotely launch your script. ssh -i key_pair.pem ec2-user@public-hostname.amazonaws.com '/path/to/my/script.sh'
5) Make the last command in your script 'sudo shutdown -h now'
Bam. Automated computing, complete with shutdown. Just make sure it stores your output somewhere. If you really can't figure it out, respond here and I can provide some code snippets later.