Since years I use slipstreamed Windows installations. This works very well, but preparing them is tedious :
1 - install a Windows with the last slipstreamed version we have (automated install)
2 - check Windowsupdate to see what's new, and take note
3 - download each new update available
4 - go to step 2 until no new update is available 5 - slipstream them into the last version we have (I already automated this step)

I'd like a way to automate parts or all of this.

Maybe a program able to know which updates are installed (already saw one, I don't remember which, and I know PowerShell can do this)... and able to download them ? Or to get them from local disk ? So the steps become :
1 - install a Windows with the last slipstreamed version we have (automated install)
2 - use Windowsupdate until no new update is available (any way to automate ?)
3 - use the magic program
4 - slipstream