I've got a couple-three spare laptops lying around that I use to mess around with Kali Linux and Wireshark and things of that sort, but lately I've been thinking I'd like to build a fair-to-middlin' sandbox for some real play time.
Who here has built a home lab and how did you do it? I'd like to hear success stories and horror stories both, and if anyone wants to proffer free advice before I start spending money on hardware, I wouldn't mind.

Yes, I searched through the forum for items of this sort, but didn't come across anything recent, so it seemed like a good discussion question to ask.