Don't worry about the crystal. Scratches can be polished out and even if it's cracked, a new one is about 40 quid.
Definitely focus on a scratch free dial, but also avoid redials.
Personally i do look at scratches on the case but even more I look at the extent of the polishing. Consider that when new an omega case had lovely clean lines, sharp edges (for the most part) and clear distinctions between brushed and polished surfaces. When a watch is polished and over polished it loses these and can end up looking like a melted candle.