@ArnoldC ... yes, I have tried Image and admittedly it's a very nice app. The only problem with it is that it takes so long to render the images. Raw takes around 15 secs. to render and jpeg's are much faster but the user cannot swipe through the images quickly even when not displaying the info. Curiously, the Slide Show works fairly well even at the fastest 0.5 sec transition. I had written to the author quite some time ago about whether a speedup is in it's future but never received a response. Perhaps I should try again.
If it wasn't so expensive I would buy it to see if it's faster but @ $7.99 it's a bit too pricy to experiment. I don't mind the price if I knew it would be speedier.
I'm working on a new App called "Qik Photo Animator" which does some of what you're after which will include slideshow, file management (including filenames, extension, skydrive integration etc).
The issue you're having with external devices on the Surface RT is that Windows RT is really locked down with regard to file access. Most of the access is via the standard libraries with full directory access only granted to a few apps (MS screens all Apps that go through Store Certification).
If you have a wish list for photo viewing/light editoring, please post it and I'll take it into consideration.
An option that's available on the Pro, but not RT, is to get one of the ACDSee products. I've been using their pro photo software for almost 10 years, and currently I'm using ACDSee Pro 5.0 on the Surface Pro, to process the huge 36MP files from the Nikon D800.
It has everything you're looking for, including RAW support, editing, management, etc. Works great on the Pro.
Downside is, it's not an app; it's a full-blown program. Plus, it's not free.
They will allow a free 30 day trial, so you could always take a look.