World-of-warcraft – Do you have to buy and subscribe to World of Warcraft

No

Once you account status goes to "Frozen" (expired) you can't go pass the main menu so it doesn't matter if you are under lvl 20 when you cant select that particular character.

What you can do is have 2 WoW accounts (not Battle.net accounts), one is "frozen" and the other is "starter", you will need to create new characters but its purpose is to check updates and chat with people. When you subscribe (unfreeze your main account) the other one will remain "starter".

Now what I don't know is how to add more wow accounts... I have 7 of them name WOW1, WOW2... The problem is I was adding them when it was 10day trial and you had button in Battle.net account "add 10d trial" any you could click it anytime. Try to find something like that.

You could also register another WoW account with different username and pass and then merge use the merge option on your main account.

Here's an easy way to play together right from the get-go.

Whoever gets the full account uses Recruit-a-friend to invite all of the other players to create their trial accounts.

Once you are in the game, the "veteran" account will be able to summon all of the recruits directly to him. While it may feel a little strange to be an Undead in the Tauren starting zone, you will have access to all the same quests (except class-specific ones).

And now with the advent of automatically learned skills, you don't even need to worry about not having a trainer nearby!

There is one potential drawback: Recruit-a-friend gives you all a 300% experience boost. You will gain levels very quickly, and as new players you may find the learning curve a bit steep.