Ours is 950 and 2.4m long.I think as far as looks go, it depends how long the island is. If it's a very long island and less than 900, it would look out of proportion. Likewise, if it's a very short one, it would look wrong to have the width any more than 1m wide.

I think one of your key considerations will be what to do with the flue / chimney. My personal thought is that you should look to punch it through the wall and keep clean lines inside, but not sure if that is feasible for you. Otherwise you might want to make a feature out of the chimney enclosure - use it to break up the length of the room. The path you choose here will inform the remaining design decisions. You have to keep in mind that an off-the-shelf fireplace unit is not going to have heaps of flexibility in terms of altering its design to suit your space. If the unit you are looking at is designed with a vertical flue and you want to punch through the wall instead, you are going to need specialist advice to make sure that the gas certification for the fireplace unit is not compromised by your alterations - or chose a different unit that suits your needs.

another option to consider with the island made up of 45cm deep cabinets with a 30cm deep knee space and tall shallow cabinets or shelves for storage...and, with a small space, a smaller island is more in proportion but still allows for reasonable walking space all around the island especially when stools are being used

Can you post a floor plan and a couple more pics? Do you need to the space to have functionality eg bookcase, study or just look appealing? I’d lean towards a long credenza, you may need to put two together and what house doesn’t need storage. I’d hang artwork above.