The mana value of a token that isn't a copy of another object is 0. A token that is a copy of another object has the same mana value as that object.

If Lavabrink Venturer somehow has no choice made for its ability, its last ability grants it no protection abilities.

You choose odd or even for Lavabrink Venturer before it enters the battlefield. There's no point at which players can target it before it has gained the appropriate protection abilities.

For spells with in their mana costs, use the value chosen for X to determine the spell's mana value. If a permanent or card in any other zone has in its mana cost, X is considered to be 0.