The sink doesn't have to be inside the room if you don't have space but maybe just outside would be great. And if you store equipment just outside as well that will mean more space inside for tanks. If you can, try to organise plumbing for water to get to each tank and to go out of each tank you will have a top notch fish room. For my fish room I'm planning on drilling every tank with an overflow hole somewhere near the top which will then be connected to a drain system. And also under every rack I'll set up some plumbing to allow me to siphon a tank directly into a drain without using buckets.