I think expresso wood works when they are already too many wood pieces in the room, and every room can use a little black. I have a lot of mahogany colored wood in my family room, so I am ordering my red ottoman with expresso legs. I have goldish metal end tables to go along with it. The end tables are round, the ottoman will be square. Variety is the spice of life..........and decorating!

I know some people like to think there are. All rectangle, all espresso and a little bit of 1 metal. But I think you'll find it ends up being a boring space.

You'd probably need to do a mood board, but the wood and metals you've described sound very nice. They are all warm colours and I think they play well together.

Another factor is the size of the pieces. If you've got a giant coffee table, and a tiny tv stand, for example, they may not work well. But if it's all giant, you might be overwhelming your space.

What do I know...but...

for #1...there is no other shape of TV table than rectangle, so it makes sense that you ought to be able to mix other shapes with it.

for #2 I think that your bronze table is pretty close in color to your espresso wood, so it won't really read as a different color/finish, but a different texture. If that makes any sense.

I'm not a designer, but my personal rule of thumb is to choose one metal, and one wood tone. I definitely don't see a problem with having both woods and metals. In my living room, all the wood (except the cat tree) is espresso, and most of the metal is chrome. I'm not saying you can't mix woods or mix metals (many folks do it successfully), but I think it is easier for design amateurs like me to limit the variety.

On shapes, I've definitely seem rooms that go overboard with rectangular. A room where every shape is a rectangle can be a little...severe (that's not quite the word I was looking for, but close).

I've become a big fan of putting together a virtual room (using whatever software you have available--Word and PowerPoint do the job, you don't have to be a Photoshop expert) to see how various elements work together.

In my living room I have square, round and rectangular. They all play well together. All the wood is different in color and yet they go together. Nothing was acquired at the same time. Trees in nature. Who says that color doesn't go with that?

Unconsciously I've chosen all black for lights, both table and hanging. Never occurred to me to match, but there it is.

If you really don't like a visual combination of finishes, it doesn't work.

The big rule I follow is that whatever I mix it can't be close to 50-50, the combinations need to be uneven. Other than that I think it depends mostly on what you like.