While I agree with the other answers, I think they somewhat miss the point. The question specifically asks about reinstalling Windows which is what I'll address here. I'm deliberately ignoring installing optional applications as they are not mentioned in the question and are already covered in the other answers.
There are a few ways to automate the installation of Windows so you don't have to "babysit" it.
1. Unattended answer file.
This is by far the easiest and simplest method. It is basically a text file (well, XML) that provides preset responses to all the questions asked during setup, so they are entered automatically.
https://technet.microsoft.com/en-us/library/cc785644(v=ws.10).aspx
(The above link provides the basics of how it works, there are various articles detailing specifics for Windows 7+)
2. Preinstalled images
Much like Norton Ghost used to do (and various other modern alternatives), all this is an image of a disk with Windows you have already installed on it that gets copied in whole when you want to "Install" a new machine. This is very similar to the "Factory restore" images that manufacturers supply with their machines - only when doing it privately, you have to manually install drivers afterwards if the "source" and "destination" machines differ sufficiently. For the most part, stock drivers and Windows Update are sufficient, especially if combined with a USB stick with a set of drivers for the big vendors - Intel, AMD, nVidia - most of them release unified driver packs these days that cover all recent products anyway.
3. Automated deployment
For larger-scale operations some companies use a centrally-driven auto-deployment system. In essence it's a combination of either 1. or 2. above and a central image repository and network booting infrastructure. This can cut down the entire install process to as little as start PC, press F12, press Y, but is quite a lot of effort to set up (though not entirely prohibitive for a superuser)
Of the above, most don't deal with the issue of installing Windows updates afterwards. As others have suggested, slipstreaming Windows update into your install disk itself is the most widely used method, but this means you do have to update your install disk/image regularly. Alternatively, switch to Windows 10, where Microsoft updates the images regularly, or use one of the slipstreamed "rollup" images you can often get via P2P (note, you can get "untouched" ones that do not have any pirated/cracked software on them, only genuine Microsoft updates, though even those are dubious in their legality)
In itself, none of them deal with licensing either, but most Windows installs will complete with an invalid or trial key or no key at all, allowing you or the user to enter a legitimate CD key and activate the product anytime up to several months after installing it.
Of course, if you're paid by the hour, having to babysit the machine all day might not be a bad thing.
Footnote: Technically, above-board "computer repair companies" can only legally reinstall Windows using the license and media that came with the machine - i.e. doing a factory restore - or using individual licenses. Installing your machine using my CD, but entering your license key, is legally ambiguous. Nobody would ever do anything about it, but I wouldn't do it on work time either.
