Yeah there can be as many units/buildings as there is space in the ui. This means there can be a max of 9 capitals, 9 frigates, 9 cruisers (note that cruisers and frigates are the exact same, but just shown in two different places in the ui), 9 logistic mouldes and 9 strategic modules.
Also you can make any unit from scratch, depending on wath you mean with scatch though.