Is it possible to use 102 as a caddy + ether and Usb?

Things who can do more can also do less most of the time. In this case once you shared are configured, you don't have to go to the interface. You also could configure everything from SSH if you want to. That said, I don't think the NAS will go any faster if you disable those services (honestly apache web server isn't that ressource hungry, although some people seem to think so and use lighthttpd or nginx instead). I don't think you can use the NAS as an external USB disk, you will have to use network to access it, USB is for backups so I don't see how you could do any simpler than what the NAS is already doing.
You can't disable the operating system, without it, the NAS isn't worth more than a paperweight. It's the OS that handles network, hard drive detection and sharing (amongst other things). You can shut down things from the web interface but it won't really affect overall performance I think, nor ease of use. So I don't get the idea. Can you develop your thoughts ?