Yes, that's a great looking perennial, I'll have to check into some of these newer types, a local greenhouse tends to get many in, costly of course, though gems are always worth their price!

Use one pair for each window. You don't have enough space on the outsides for two panels on one side.

When we had a new water heater installed and had that problem, we were advised to turn off the "main" water supply valve and open all of the taps in the house, then to very slowly turn the water back on, taking 5- 10 minutes to fully open the valve. Turn on slightly, let it run for a couple minutes, turn a bit further, let it run, etc. ETA- I think it had something to do with removing air from the pipes?

Looks like classic efflorescence. or latex leaching. efflorescence?\ You can try a low dilution mix of Sulfamic acid crystals.. (once ) . After it completely dries out for a few days you can go over the grout w an color match epoxy based grout colorant to try and supress it. Common reasons for efflorescence A. To much water used in the grout installation and clean up. B. Too much water used in the shower pans screed mortar C. Using the Wrong type of screed Mortar. It will never fully go away and require constant work to maintain. Acids only work once or twice and also break down the grout with successive use as will distilled vinegar.. Latex leaching occurs when the wrong type adhesive is used thats not rated for wet areas. Its hard and crystalized? Id guess its efflorescence.