There are many styles for your portfolio layouts. You can do one column for those categories that you may not have as many photos for, and do multi-columns for those that you have more for.
This layout allows the viewer to soak in each project, one at a time, and gives more real estate for each photo. The layouts with many photos tend to give the user lots of options, while allowing them to click on each to enlarge and see all the details. The small thumbnail piques their curiosity, while giving them a wide variety of projects to soak in.