Hi Chris.
You can use SPPB in Cassiopea. But this requires some CSS adjustments of the component area. You cannot get full width section without adjusting the template even using fluid layout.

If you want to use Cassiopea add this code to /media/templates/site/cassiopeia/css/user.css (create this file and add code there)
.com_sppagebuilder .grid-child.container-component {
grid-column: 1/-1 !important;
}
.com_sppagebuilder.view-page .sppb-row-container {
padding: 0 !important;
}
Just an opinion. Cassiopea is a much more flexible template for building any layouts if you have CSS skills. I wish the Joomshaper team to finally consider using CSS Grid in their products instead of Bootstrap Grid