How to get started in postmarketOS?

The main website suggests "getting a second-hand SDM845 or MSM8916 device".

While I am fine with getting a second hand phone for this (as long as it doesn't cost as much as a new one) I see many devices with those chipsets that only partially work.

I am fully expecting this, but due to having been in the Android modding community in the past I know it is extremely common to abandon devices completely at random times. Since for this project I am willing to spend money on a dedicated device, I don't want to make a purchase I'll regret because they decided to move on to a newer device (or disappear from the internet completely).

I am not looking for a device with "perfect" support, as I feel like that would be useless. I want a device that works already well enough but that I can actually contribute with.

My own Poco X3 NFC seems good for this, but I don't think I want to commit my main smartphone yet. My older smartphone, the ASUS Zenfone 3 Laser, is completely unmentioned (but the base model is). Maybe I should simply use the latter and contribute by adding this extra device, or is it better to get something like a Google Pixel 3 or Motorola Moto G4 first?