Honestly, the value proposition of old business computers is almost unbeatable.
Yes, it's not the most recent hardware, but decent enough, especially the chonky boi ThinkPads are very easy to repair/upgrade and built like tanks (though only Russian ones, they barely withstand an RPG hit, which is a shame).
How exactly is SSL terminated in your setup? Usually, you'd use something like nginx or apache for termination, but I don't see that in your description?
So who exactly has the private key?