To launch Affinity Photo 2 for your image files simply type in as application path: AffinityPhoto2
Since fotoARRAY does not check for EXE extension or the existence of the executable you can send files to Affinity directly.
Other programs do this kind of check and will not start Affinity. Here you can use the tool Start_fotoARRAY.exe which is installed by the fotoARRAY setup. Here you can type in AffinityPhoto2 as executable and the program will send the files there if you specify Start_fotoARRAY.exe (or whatever name you renamed this EXE to) as processing application.
To use Affinity Publisher 2 as viewer for created PDF output of fotoARRAY simply sepcify
in the text field near "Launch:" in the PDF export dialog.