New to screenprinting, just have a basic Q -

I'm aware that you need room at the sides of the mesh to allow for flex when you apply pressure down. For example if your print surface is 10" by 10" you would need (I'm guessing) 16" by 16" of visible mesh? That would allow 3" all around. What's a "safe minimum" amount of room to leave on all sides?

Thanks!

Hmm, and do i need a few extra inches at the top and bottom to hold the ink, so to speak?

Leaving at least an inch all around is good.

My surface area I will be printing on will be 11.5" by 24.5" so reasonably large (i think). Will need a fairly big frame. I'm thinking 3" all around to be safe?

I would ideally allow for about 2 inches from the frame edge for stencil size. The deal is the closer you get to the frame edge the higher the mesh tension will be. This means that the resulting print will have more ink toward the center than it does near the edges.