It really depends on how the data is related. Using multiple queries when you can perform a single JOIN statement is inefficient, but it doesn't always work that way. Your PHP script logic should determine what data is presented where, it doesn't have to create a query at each segment.

The bottom line is your skill level and the amount of traffic you expect. Once you progress and have worked with SQL a bit you can refactor all your code to be more efficient. By that time the site may have so much traffic you'll be forced into optimizing everything.