Welcome to the club!
The build sounds good, and yes a little bit overkill. I host way more on much older gear, comfortably. For “homelab” stuff I wouldn’t buy a Xeon like the other commenter said lmao, you’re not going to like your bills. That’s way too overkill as you’re mostly likely going to be memory-bound, not CPU-bound.
Just for reference, I have ~65 containers running and using ~8 GB RAM. I started with 8 GB and added another 8 GB to have a bigger buffer, and to try out new stuff from time to time.
In general, don’t worry about hardware too much, get what is within your budget to build up knowledge and skills. You will figure out what you need later down the line.
Also, I prefer Adguard Home over Pi Hole, and check out Vaultwarden, the community Rust version of Bitwarden as well.
I think it’s still good to go with the HDD instead. You can always later get M.2 SSD with a USB enclosure if you run “busier” databases that will benefit from faster speeds. They’re small enough to dangle from USB ports.
When you go refurbished it’s always luck when it comes to any type of storage. My server’s root fs runs on an SSD that’s like 10 years old, yet I bought second hand hard drives that are 4 years old and they were broken beyond repair.
Make sure to backup your stuff regardless.