The Do's: If you sincerely enjoy and get enthusiastic about other likeminded individuals picking up physical media. I think this is imperative when doing mail order/distro, because without that natural enthusiasm, you probably will not enjoy it and find it to be like tedious "work".
The Don'ts: If you're setting up distro/mail order with the intent to turn a profit you might be disappointed and most likely will find out real quick that in order for mail order to stay in existence, is that it absolutely has to coming from a place of pure passion and in my opinion this is how mail order should be established under those types of terms and conditions. Those seeking to turn mail order into some type of extra income or side hustle of sorts, should view it more so as a hobby. The reward is being able to contribute back to what you enjoy most.