Concurring with that, a distro IS the community, remember

To build a small distro as a learning experience, I would suggest to use busybox (or toybox or tools from suckless.org, heirloom project...).
If you build a statically linked busybox with most of the options, you end up with all the tools needed to start an run a small distro. Busybox is easy to configure (make menuconfig, ...).
If you choose this way, building a small distro boils down to:

• Build a file hierarchy and create a few nodes in dev
• Compile and install a kernel
• Install a boot loader
• Compile and install busybox
• Create an init script

I'd suggest to build all of this in a disk image. A disk image can be mounted, chrooted in, ... AND in the end, you'll be able to boot your magnificent Linux distro in a virtual machine (qemu, virtualbox, ...).

You can create a raw disk image with dd (or qemu-img). To mount it, the easiest way is to use 'losetup'. I you use qemu, you can use the raw image directly. With virtualbox, I'm not sure, but I think you would need to convert it first (there are tools to do that).

I don't have time to add much more on this, but I would suggest to look at Pocket Linux. Interesting stuff I know of can be found with Alpine Linux, Aboriginal Linux, Morpheus Linux, Sabotage Linux, suckless.org and many more I forgot ...

It isn't plug and play, but it can still be done and done easily, even on windows.

Windows Process: Use System Image Manager to create an automated answer file for the setup sequence, build the system, copy sysprep with the answer file over to the machine and then run "sysprep /generalize /shutdown" and make an image of the machine.

Linux: Build a kernel for the target, copy modules, rm the udev database and set it generate the hwdb on first boot, make sure /etc/fstab and /boot/grub/grub.cfg are ready and the grub bootsector or efi chainloader is in place. Very similar process for BSD.

Forgot to add, if you really are interesting in cross-architecture compiling then Cross Linux From Scratch is a good place to start.

Yep that's the stuff I'd like to learn to do. Any good reading resource on how I'd do those things?

I don't know about one site giving you everything neatly packed. I started with the Pocket Linux Guide I mentioned above changing the floppy disk stuff with a disk image. After that I did a lot of googling and reading to get further and have a small distro with network, etc... Most of the info you can gather on the web is about making embedded Linux stuff. Have a look a the web site of busybox and the various sites of the linux distro I mentioned above.

Right now, I'm too busy to give you more info. I have some notes on all what I did. Let me know it you're still interested and in a few days, I'll post a basic guide to get started.

[Edit] I found back another useful howto I used The Linux Bootdisk