Question, when going back to a free account from a sub. Can you still use any character you have created as long as they are level 20 or below? I am not planning to renew my sub which will end in late November, so am curious if I can make a new character and lock at level 20 then continue playing as them just fine.
Side question, will I still have access to the Vulpera since I have them unlocked or will they re-lock?
Yes but you’ll be restricted heavily. Can’t whisper others, mail, etc.
I remember being able to use mail when I was playing free account before I got the sub. But even so, if I can remake my vulpera main here, I can transfer my gold over and what not. Should be fine.
last I heard they couldn’t…for the purpose of preventing bots from spamming players inboxes.
Ah, maybe can’t send but can still receive?
You are able to play any character up to and including level 20 but not more (including vulpera!) 
So I would recommend level-locking whoever you want to play at level 20 so they don’t go over and you can still play them. I think there’s a gold limit of some sort but I don’t know how that is impacted sorry. 100% sure you can still play your vulpera because I could still play my level 10 mechagnome twink when I didn’t subscribe.
I need to remake my vulpera. This one is level 60, which is fine. The gold limit isn’t a big deal either. I just needed to make sure I can make a new monk to keep playing as and lock him at 20. As well as my other characters.
You can also make new characters (up to the 50 character account limit) when you go back to the free version too!
Sounds about right, but you’ll have to try.
You can’t use the mailbox at all, from what I recall. If you get anything from the Postmaster, you can’t claim it.
Correct. You will get notifications you have mail, but you can’t use the mailbox. You can’t initiate whispers but you can respond to someone else. You can’t use the AH or trade with other players.
You don’t have to lock your level. Your characters will continue to earn xp for 10 more levels, but it won’t be applied until you reactivate the account.
The only things you will be able to buy are vendor items.
Support article has your answers!
I have experience in this as I have an account whose sub I let lapse a while ago which I still occasionally hop on.
You can make characters of any race you have unlocked including allied races.
You can log on to characters level 20 and below. And level new ones up to 20.
You cannot whisper people who don’t have you added as a character friend (or who whisper you first which allows you to whisper them back until they log off).
You cannot talk in global channels.
You can talk in say and emote BUT anyone say 10 levels higher than you will not see your chat.
You cannot engage in trades with people.
You cannot use the auction house.
You cannot invite people to groups though you can be invited to a group.
You cannot use the mail system at all. Sending or receiving, you cannot even pick up system mail like say anniversary packages or postmaster stuff. It shows up as there but you can’t access it and it will eventually expire and be deleted.
If you were in a guild before you unsubscribed you can remain in that guild and use I believe guild chat and such. If not you can’t join a guild.
You are capped at 1000g max you can earn. However you are grandfathered in with whatever gold you had before you lost your sub. So for example if you load the character up with 80,000g they will continue to have and be able to spend 80,000g including amounts over 1k on single vendor purchases (can’t use AH or trade as I mentioned), however they will not gain gold, copper, silver, etc until they fall below 1000g again.
I also believe you can’t engage in pet battles on an account without an active sub but I can’t recall conclusively.
In other words you are for the most part locked into whatever you have on that character when your sub expires and can only change what you have on that character if it can be bought from a vendor or drops from a mob you can kill at level 20. You cannot trade, use the auction house, or mail. You can only whisper or for the most part talk to people who already have you added as a friend.
You are locked out of a lot of things though a lot less than you used to be before the level squish and chromie time which has brought a lot more things in reach.
Unless it’s just for social purposes or RPing I don’t see much of a game at level 20 to be honest.