Photoshop questions.

[Midgardsormr]

Not so fast! Scaling up might actually be possible, depending on how you're doing things. If each texture is seamless and fills the entire document, you could simply crop down to the room you want, increase the canvas size, redo the texture fills, then scale up each layer mask. Even better, if you've used paths, which are vector shapes, to build your masks, you can scale up the paths and reconstruct the masks. End result: the textures will be exactly the same, but the masks will all be resampled.

Or, as Lukc says, you can use Smart Objects. If your original textures are 300 dpi, then you scale them down to 72, as long as you don't rasterize the texture layers, you can scale back up to 300 with no loss of quality. That will require you to scale each texture by 24% in your 72 dpi document so that they'll return to their original resolution when you go to 300. Make sure that they're Smart Objects, though, or that won't work!

edit: Concerning your bevel issue: If the layer is bigger than the canvas, then the bevels will be outside of the visible area. You can either make the layer bigger or trim the canvas at the end of the process.