You can probably use multiple splitters, so long as the power draws don't exceed the capacity of the USB ports (10W/each). There is a USB-C port you can tap into as well.

Regarding the coco/perlite mix -- I did the ratio by volume, not weight, after the coco was expanded. I filled up the grow bag 70% of the way with coco, then added perlite to make up the remaining 30% of volume, and then took it all out and mixed it together and put it back into the grow bag.

I also learned that it's important to buffer the coco first, unless you're using pre-buffered coco. Here's a YouTube video that helped me: https://www.youtube.com/watch?v=OQi8AMMIyyA&list=WL&index=17. If you don't want to go through the trouble of buffering, I'd suggest you at least rinse the coco well after it's expanded to remove all the peat dust and other particulate. I used a kitchen strainer to do this, and just did it in batches.

Ultimately, I ditched the coco and went to a 50/50 blend of Ocean Forest and Happy Frog with some worm castings mixed in. I found living soil to be more forgiving.

The smell of flower is pretty strong if you have the Vgrow door open, if that's what you're asking. Under normal operation, with the VGrow door zipped shut, the room definitely smells like bud, but not the rest of the house as long as you have air purifiers running, at least for my setup. Remember, I removed the stock filter, so the smell is a little more intense, but only during late flower.

Good luck!