.. When you just can't manage to stay away :)

[Obi2Kenobi]

Definately no on the fire skill. They require many points to be able to have any effect in Hell/late nightmare. You should probably also keep your summons to a minimum of points, just saying you can chose between the two without feeling "wasteful".

And now, for my long article on the Cow Level (actually, it is my shortened version with only the relevant parts contained...):

There are, however, certain flags to determine if your character is prevented from ever making a cow level in a certain difficulty again (but you can still go through the Red Portal made by other players).
a ) You kill the Cow King.
or B ) Someone in the Cow Level (contrary to popular belief, it doesn't matter if s/he is partied with you or not) who has not already killed the King kills the King with you in the Cow Level. If the King killer has already killed the King in a previous game, you will still be able to make the Portal. If you are partied with a killer who hasn't killed the king, but you aren't in the Cow Level, you will still be able to make the Portal.

So you can take the portal however many times you want, there is only a restriction on making the cow level.