Well, you could try one LVL and if it collapses, then rebuild the floor and use two.
It really depends on how much stuff you have in the room above and how solid you want the floor to be. Do you care if the floor bounces when you jump up and down?
I doubt that a 20 foot wall is not load bearing. What is holding up the roof? If you go into the attic, are ...
It's always smart to ask when dealing with support structures in a building. I'm not an engineer but based on my long experience in dealing with various structural issues attaching screws of that size to the bottom of a 6x8 beam to hang a curtain is not an issue. The assumption, Of course, is that this is a standard curtain and not made of chain mail.