Hi Fil,
It’s not possible to display portfolio items in a grid with Simfo. You could, however, use posts in place of portfolio items to serve your purpose.
We also have a variety of themes that display portfolio items in a grid in our repository. As you’re on the WordPress.com Business plan, you’re free to experiment with different Premium themes at no extra cost. I encourage you to use the Portfolio filter in our repository and have a browse about to see if another theme catches your eye:
https://wordpress.com/themes/filter/portfolio/
Qua is a good example of a Premium theme that has portfolio items arranged in a grid and the option for you to add some introductory text. I personally really like the look of Mellow too.
Let us know how you get on with the above or if you have any extra questions.