I am a fabricator. I don't believe any of the things you are concerned about are real issues. Many natural stones have fissures. It's VERY common to notice features in your installed countertops that you didn't see in the slab when you picked it. (This even happened to me and I look at stone every day.) The gap in the back is very acceptable assuming it'll be covered by splash. The sink cutout variation you see is very likely the sink, not the cutout. Most shops today have CNC's that make cutouts that are accurate to very small fractions of an inch. Overall it sounds like you have really nice new counters that you should enjoy. FYI Bianco Antico is a very chippy stone that takes extra fabricator skill and effort to finish well. Sounds like you had a good fabricator.

Look at grays and taupes that you find in the stone. Try to find some paint chips that aren't "cold" as some grays and taupes can be. Gray is such a wonderful neutral, and it would probably go nicely with your wood. The thing I love about this stone is that there are so many colors that go with it, you just have to work with your cabinet color too. I cannot wait for you to post pictures of the BA installed. To be ensconced in Bianco Antico, ahhhh wait you said "used", does that mean it's installed? If so, post pictures!!!!

I am a fabricator. "Brand has no bearing on chipping; it's all the same stuff." for quartz this is exactly correct. For the harder natural stones a well rounded edge provides substantial protection from chipping. You really have to whack a rounded edge to chip it. Occasionally, even in hard stones, an inclusion can pop out. If you manage to save the popped out piece the repair is simple. For other chips the repair is also relatively simple with the fillers and tools available to the fabricator AS LONG AS the customer has realistic expectations. If you follow Joe you know he spends a lot of effort making sure the customers expectations are realistic before he starts a job. For softer stones like marble and travertine chipping is a greater risk simply because the mechanical integrity of the stone is much less than granite or quartz. Repairs can also be more challenging as matching light colors or white is more difficult. A trick is to grind up a bit of the stone and use it to color a clear adhesive but you have to have a scrap piece of the stone for this to be an option. All that said rounded edges are much less prone to chipping on any material. A competent fabricator has this discussion with a customer automatically as part of the edge selection process. My 2 cents.

May I suggest posting a picture of your slab? This is my Bianco Antico.