Could Lando be placed as a crewer on an epic ship? I know that epic ships aren't supposed to deal with focus or stress tokens. Lando can give evades, though.

And as a follow up, could a GR 75 obstruct the attack on another epic ship?

Lando can be used on epic ships.
Its just that Focus, Stress, and Evade tokens on an Epic ship immediately evaporate, so it's a terrible idea.

Huge ship rules page 4.

Focus, evade, and stress tokens do not effect huge ships

And as a follow up, could a GR 75 obstruct the attack on another epic ship?

Yes. There's a paragraph called "Obstructing" in the huge ship rules.