The reason tags are important is because pixiv will promote your pictures according to those tags. Otherwise it is questionable if that many people are using search function.

so when tagging your pictures use tags that other pictures with similar content use.
or you can invent your own tags if you want your other pictures to be promoted along with the current picture.

The main tags that I use on my pictures are #loli and #shota :)
using R18-G tag seem to be useless because you already set that category by default. but if you will set that tag I think it will be used with the same logic as other tags so if you do not reach 10 tag limit you can add it and anything else.

Search obviously does not look at description title.