I think it would be better if you have all the frames in line at the bottom. This will be much easier on the eye and look more orderly rather than 'messy'. The layout on the floor is more successful than the one on the wall (i.e. the A4 frame on the left is better next to the A3 frame and the top two small frames on the right are better positioned than on the wall).
Also aim to hang them so the center of all the art combined is at about 58 inches from the floor. This is a good average eye height.
I personally think the hallway is too dark to have a grey wall. It would close it in quite a bit.

Straight line along the top will make it all more cohesive and neat!

Hi Mwiess

I've seen in new houses, a recessed nook for paintings, if your walls are non masonry; that's an option, maybe two large zones that you could divide your collection. Also have picture lights or inbuilt side lighting perhaps.

https://goo.gl/images/P6xhH2

Keep us updated with this i would love to see final result!

Black & white frames look great! Here I created a pattern that fanned out from the centre in a horizontal diamond so neither the top nor the bottom line up. BTW I've put stickers over the faces to protect my client's identity.

Check out Pinterest under Gallery Wall Layout for plenty of ideas too. As others have mentioned, a tubular skylight or two as well as good artificial lighting would make a real difference to how large and light the hall looks.

If that's the case, stick to a light colour on the walls with white on the ceiling and possibly woodwork such as skirting (base) boards, architraves and doors.