Good to hear you didn't mean at the same time.

If you do want to place a 8W, be sure to stick it on the side like mentioned before and let some of the heat vent out of the top. The 4W will work just fine to though since 10 gallon tanks are small.

The lids look fine, generally the more holes the better in my experience. Good air never killed a frog :P. That's why I perfer screen or mesh tops as opposed to these nearly sealed in Viv's that people are building.