about the mirror situation and I would paint the one you have black. If you stick with this mirror, I’d have the chain painted or replaced with something as low profile as possible (to still hold the weight…smaller hooks too, since you’ll have to re hang it anyway.)
its just 2 mirrors glued together. Smaller ones will make the space feel
even bigger and give you room to hang pendants on either side of the mirror. These
frosted glass, globes will give great light to both sides of the vanity.
Answers to your questions:
I’d make the runner a 2×5 so that it can be centered under each vanity.
Here’s a frame for the artwork.. I’d get it printed at 18×22. I always take these files to Staples and they are very helpful.
I’d have your handyman look at these barn door links but he might have a better way to do it. I also linked to some doors but you might need to check dimensions.