The motherboard box comes with SATA cables. You usually get 4 or so, so no need to buy extras unless you have special use cases like need super long ones or something
The case aesthetically looks OK to me.
He's probably concerned about thin case material and sharp edges. Some of those low end ones you end up with sliced up hands by the end of the build if you're not careful Also, some higher end cases give you more cable management options so you may have to get creative if there aren't many in your current case.