I am new to editing Gigapan shots and see from a previous discussion there is a file size limit in Photoshop that my files are going to exceed (>30,000 pixels wide). I see Corel Paint is one option from that discussion but are there any other recommendations? Thanks

The 30,000 pixel limit is not a photoshop limit, but a limit of the TIFF format. PhotoShop also has the .PSB format which has no such limitation.