Welcome :)

5 is the maximum, but you don't need to use 5 each time.

Some users look at specific tags, and like to support that tag by voting posts in that category.

The most important thing about tags is to not use them when they don't relate to your post.

For example, only use introduceyourself on your first couple of posts that talk about you. Using this tag later may end up with a flag/down-vote.

I see you have used 4 tags on your latest post, I think these are all relevant - good job :)