How should we lay the LVT plank flooring to create a seamless look without transition strips and should we use wedges for expansion?

We’re currently working on remodeling our second floor and putting in LVT plank flooring. I have a bunch of questions and would really appreciate any input!

So, we’re trying to figure out which direction to lay the planks. I’m thinking parallel to the stairs, but my husband prefers vertical because of the hallway. We were aiming for a seamless look with no transition strips, but now we’re wondering if that might actually look better. Any thoughts on that?

I’ve heard that you need a good mallet hammer and blocks to lock the planks together. I’ve also read about using wedges to create a small gap between the walls for the floor to “float” and adjust. Have any of you used wedges before? Are they necessary? Should we leave a gap at the walls or butt the planks right up to them?

Lastly, we went with 20 ml vinyl flooring, which is pretty thick with a rubber backing. Our floor is mostly level, but there are a few spots where the plywood is uneven, creating gaps in height. Should we make sure the floor is completely level before installing the planks? Do we need an underlayment pad to even things out, or will the thickness of the planks do