Tags: Use of relevant tags is important from the SEO perspective. It helps the search engine track your post based on the tags you use.
Blog for the fun of it and show character. It is immaterial how many write about a particular subject, it is how you write the matters.
Formatting - Your post need not be a circus. If you are not good with formatting, then stick to a theme that is light and descent in colors and the post layout. If you are good with trying new stuff then use that skill to better express through colors, fonts and layouts. Avoid colors that are dark and fonts that are overtly bright.