You can use any. I have some raspberry pi devices (with Pi-hole installed) running on 8gb.
On a 16gb there is plenty of space for the logs. With v3.3 the logs get cleaned/purged at defined intervals. Starting with V4.0+, Pi-hole no longer uses the same logging method:
See What's New With FTLDNS?
I'd still leave this on for troubleshooting purposes. If you set-up the devices for your family members, allow yourself remote access for any eventual troubleshooting .
You could, however there are a few things to keep in mind:
- your SD cards have to be identical, as in capacity/sectors/cylinders or card #1 slighlty smaller than #2 and #. If your card #1, the one you'll end up cloning (let's call it master) is slightly bigger than card #2 or #3, cloning will fail.
Initially you have to create an image 1:1 of the master card. That image is saved as-is from the card (partitions, files, settings, SIZE). Then you'll have to "etch" that image onto the slave #2, #3 SD. It won't let you write it if master image size is 1000.1MB and the slave size is 1000.0MB - You are setting up Pi-hole on your network, with your network configuration (IP's, Gateway). If your family members' network settings/parameters are different, all your pre-defined settings will fail when they plug it in on their network.
Any well established brand will work.
This can be debatable but overall, the best combo is to use the power source that comes with the raspberry.
It's not automated. The admin page will inform you if an update is available and one can update it from the command line (hence the remote access thing I was telling you above).
Yes. It would require a little bit of setup (port forwarding on the local - where Pi-hole resides- gateway).
Follow this guide:
https://www.raspberrypi.org/learning/networking-lessons/rpi-static-ip-address/
That is indeed a good idea to avoid any possible conflicts. It's not mandatory however. You can set-up the ip on the raspberry and use address reservation from the router also (for the particular MAC address of the raspberry).
This will answer your question:
I don't know that. A pretty standard configuration for the LAN should be included. Shouldn't differ too much from your Nighthawk, or any router for that matter. See if you can find the gateway model number manual and go through it to get an idea of how things looks from a configuration perspective.
You could use Unbound with Pi-hole.
Have fun and happy tinkering !!!
No problem. We're a FUN community.
Your writing was just fine 
Didn't noticed a thing being off