Woohoo! Successfully installed a website using the Streams repository and a single shell script (based on the one available in the .homeinstall folder of Zap)! Or almost, a few things had to be done manually.
Only tested it with Nginx using localhost, can't see why it wouldn't work using a real domain name, I'll test this as soon as I can. Should even work better.
Only "major" issues I have are related to Composer. When run from the script I get a message telling me the command is unavailable (while it can be found in /usr/local/bin/) and when run manually there's a message saying that it can not be run by root, which is actually possible after answering yes to a prompt. Figuring this out should just require a little extra time.
If you feel like having a look at it, the script can be found here