If The Wandering Minstrel would enter the battlefield at the same time a land you control would enter the battlefield tapped, that land still enters the battlefield tapped.

The Wandering Minstrel's second ability checks at the moment it would trigger to see if you control five or more Towns. If you don't, the ability won't trigger at all. If it does trigger, the ability will check again as it tries to resolve. If you don't control five or more Towns at that time, the ability won't resolve and none of its effects will happen.

If a land has an ability that says it enters the battlefield tapped, you choose the order in which that ability's effect and The Wandering Minstrel's effect apply. This means you can choose to have the land enter tapped or untapped. If a land you control is simply put onto the battlefield tapped without a replacement effect being applied, it always enters untapped if you control The Wandering Minstrel.

The value of X is calculated only once, as The Wandering Minstrel's last ability resolves.