If you leave the Collections separate and use CSS then you can use the Add feature to repeat the fields for just that collection, whereas if you put them all together you would be repeating all fields

You can use the standard CSS for displaying the Collections side by side. The #q numbers are for the Collections, not the fields that appear in the collection.

Based on the width of your form and fields you may need to make some adjustments for the labels and Fields widths. When using the Width:50% in the line below it is shrinking the widths of the fields as well but is the easiest way to split the page

#q8, #q10 {display:inline-block;width:50%; vertical-align:top}