@Duo35
You've done a good job with the coffee station, so I definitely think you have the ability to improve the arrangement of items in the house. It maybe just seems overwhelming as there are a lot of rooms and quite a lot of stuff.
You could just gather all of the bits and bobs and put them in one room and have a good look at them. You may instantly notice things that work well together and can start grouping things. Or, you might just stare at it all for a while and then run away!
If you think the latter is more likely to happen, try to break down the task into more manageable segments, e.g. start with a particular category.
One thing I noticed is that there are quite a few pictures and other things displayed on the walls, but a lot of it is scattered around, sometimes in a seemingly random fashion which looks 'bitty' and not very effective. Also, I don't know if a tall person hung some of these pictures but a lot of them look too high (my dad was tall and always use to do this). Pictures should, in general be hung at eye level for an 'average' height person.
That is, unless, you are creating a gallery wall or grouping. I think that, unless you have large, statement pieces of art, or just need something for a small area, pictures (and other decorative objects) often look better grouped. Look for similarities and a theme (coastal would be an obvious one in this case) and see how they look grouped together.
You can lay them out on the floor and move them around until you find an arrangement that you like. If you are still not confident about putting them on the wall at that stage, use brown paper or similar and cut pieces the same size as the pictures, then use making tape (or something else that doesn't cause damage) to stick the paper to the wall. Once you are happy with the position of everything, you can start hanging the actual frames.
If the artwork itself has colours that work together, the frames do not need to be matching. An eclectic selection can work very well as long as there is enough variety. Or, if you think that looks too busy or messy, you could always paint the frames the same colour. This takes next to no time to do. I quite like painting frames the same colour as the walls (if the walls have colour on them). That can look very chic.
I don't know what has been used to hang the pictures, but if you are not planning on filling and repainting walls, you might want to think about hanging your groups of pictures in areas where there were already some frames hanging so that you can cover up any holes.