The directions that comes with the sink should have the recommended locations for the pipes, if you leave them the way they are you are going to be pizzed off ever time you look at them, your choice, luck.

the bad section of pipe needs to be replaced. There is no other permanent fix, especially in a concealed location.

We have a Kitchen Aide 3/4 hp and it has worked extremely well for the past 15 years. This year it is finally having a little trouble but my husband worked on it and said that a tiny bit of rust had caused one of the blades to stick. He unstuck it somehow and it is working fine again. It does seem large under the sink but have never had anything else so I don't really know the difference. I know that it can handle large amounts of waste when I'm making vegetable soup or something like that with a lot of peelings. I can't think of anything I don't like about it. Mine is pretty old though and so I am not sure how they are now. I've been told not to get anything less than 3/4 hp. I would definitely get another KA if ever in the market again. Everything in my kitchen is KA and so that is the only reason I got it to start with, I was ordering appliances when we built the house and just stayed with all one brand. At the time 15 years ago, KA was considered a very good brand. Now there are all sorts of choices out there that I think only makes it more confusing!!!

Kerdi is a complicated waterproofing set up that is just not needed in a residential non steam bath. It actually creates more possible issues with adhesion and you would have been better off just hanging a plastic sheet behind the cement board. Problem you have now is if you pull some tiles you pull the Kerdi. Scuhluter is one of those products that is promoted all over the internet and the Co uses forums to promote their products. problem is DIY'ers don't have the skill set or experience to use it. Any pro using it has had to test their install methods as you have to be assured that it is adhering to the wall. I just don't get why with all the roll on waterproofing methods outside of a steam shower or a high-rise install. It might sound crazy to a DIY'er but I would redo the smaller wall. Yes you will disturb the Kerdi but you will also correct that gap issue. Move the tiles over to the left by cutting the lowest one the size of the gap on the top and then run a plumb line from the outer edge of the lowest tiles right side edge. This will have you cutting the tiles up to about midpoint and then you should have the correct grout line. I think the corner upper portion gaps are just too big. A trick to correct uneven gaps is to run two pieces of tape parallel to each other using the widest gap to space them. What this does is make the gap look uniform top to bottom. Use non silicone color matched caulk and do in two steps First as just a fill for the gap and the second as the finished bead. The bead has to be pressed down after you pull the tape or it will lift off. Good luck and spending time now will save you a lot of work later. Even pros have to redo jobs. Where is the shower head?