Definitely going to use a walkthrough if I can find one. You get the same story and it's a lot more efficient that way. It's also easier to just play the routes you want.
AND returns results only if all specified tags are present in the visual novel, OR does it as long as one or more of the tags is present.
AND only excludes visual novels if all of the listed tags are present in it (in combination). OR excludes visual novels if even one of the listed tags is...
It really depends on the story. If it's a lighthearted story I prefer green flags, otherwise one or two red flags in a serious plot is pretty exciting.