That's wonderful. No, definitely DON'T do any resizing or cropping or anything. Just place the PSD files directly into your layout, exactly as I taught you in the Layers & Masks Class.
No, it's absolutely fine. In fact, the noise layer is too strong, it only needs to be 10% opacity, not 20%.
If you're seeing banding, it's a problem with your screen or calibration, not your file.
It's not overexposed, not by a long way.
If it looks overexposed to you, you have a serious problem with your screen. I urge you to invest in a monitor calibrator as quickly as possible.
You must NEVER do that. Lightroom is a raw program, and all raw processing must be done BEFORE Photoshop work, NEVER after.
You must apply the filter effect in Photoshop. Show me what the filter effect looks like, and I'll tell you how to do it.
Furthermore, this.
I know it will be of little comfort when I say that you're not the only person this happens to.
Even less comfort when I say I don't know why it happens!
First, I'd recommend doing this.
Sure! I look forward to helping you, these are fun.
Post your photos once you have them.
Remember, this kind of work lives or dies by the photos you take. Get the lighting as plausible (matching) as possible, and think carefully about the angles and the depth of field.