Hi @Shand359 - for handling FITS files, there is also:
Fitswork - specifically for FITS files. Great for quickly browsing/viewing FITS files. Can save as different format (TIFF etc.)
Irfanview (there is a plugin for FITS format and many others) - it has a batch conversion utility which is handy (can convert to TIFF, JPG etc)
+1 on the PixInsight comments above. Photoshop is also complicated (esp. for astro pix processing). If starting from scratch, would prefer PI over PS. Some use a mix of both.
DaveNL