The gameservers are Provided by XEVANIO.DE, a realiable group which offers good hardware and good support. Crashes due to bad hardware are very much unlikely and almost impossible to happen. Something that can cause the gameservers to crash is using models from hat/charms plugins on maps in which they are not supported.

We have a constantly updated list of maps, that you can find here, which has hats/charms/graves/hptank features all disabled to prevent these crashes. That's the most common and probably only reason why the gameservers would crash in the first place.

After a crash send an email to admin@l4d2enhancedvanilla.com with all the needed information such as the campaign and map name (VERY IMPORTANT), game difficulty and number of players.
You can also report the issue on the official steam discussion.

Intentionally using models to crash the gameserver will result in a permanent ban.

The gameservers can be joined by either directly connecting to them using connect command or server browser, by connecting through the steamgroup server browser (if you are a member of the steamgroup), or by using a lobby by first inserting
on console and then starting a lobby with your desired map.

If you entered the server directly using console or server browser, other players must do
the same if they want to enter, and they won't be able to join through lobby or invite.

If you want other players to join from lobby the server must first be entered from a lobby.
You can join it from a lobby by inserting
mm_dedicated_force_servers, on console
and then simply creating a lobby and starting it with a map that is available on the servers.

Players are allowed to use vocalize commands in L4D2 Enhanced Vanilla.

This only changes when players start spamming vocalize commands too much. In that case, you won't be allowed to use it for a short period of time. To use vocalizer again you must not vocalize anything for a bit.

Continuing to use vocalizer while muted will delay it's reuse even further.

No you don't. VIP is completely free and can be obtained by simply joining the steam group.

One of the core features of the L4D2 Enhanced Vanilla gameservers, is to provide a bug free
experience by fixing unpatched exploits.

Bunny hop is an exploit that allows players to achieve speeds that they shouldn't be getting to. This can lead to out of bounds sections in maps, or even breaking their events.

Furthermore it basically grants the players a speedhack, which no matter how hard it is to pull of, still remains a speedhack.