One of the risks of trying to accomplish too many things is missing the details. The more projects you take on the more details that have to be addressed.
One way around this is to have a number of project managers. Each project manager is responsible for a specific project, division, department or job. The project manager deals with all of the details and the overall manager is responsible for the project manager.
If you utilize your project managers properly, bringing on more projects and more project managers will make your job much easier.
The key is to hire the right project managers, realize that the ultimate responsibility still lays with you so you have to do more then hope things get done, and continue to monitor and manage on a regular basis.
When you get the right group of project managers, the ability to take on more projects becomes almost limitless.
Have a great day!