I still have a lot of experimenting to do but this looks promising.
I purchased a WD My Book World Edition NAS. It has an option to expose Linux via SSH. So far I can log on and view directories on the iPad using an iPad SSH client. I am hoping that I will find a way to use an existing Perl script that I have to copy photos from my camera's SD card to a shared directory on the NAS.
I have two printers on my network with SD card slots that can be read over the network.
Once the files are on the NAS I can use an IPad uPNP client to view the images. In fact WD has an app called WD Photo that seems to work quite well.
It's early days but I think that I can make it work.