I'll address the few I can:
I've seen this frequently. More often shown than not shown. On reviewing business cards to look for someone for a task, those with a short list of services get a better chance.
Double-sided are now the norm, so much so that I don't think they're a real advantage any more; unless you've some striking branding or similar to put on the back.
Horizontal every time. Once that card is in the card organiser or folder it must match all the other cards. Nobody wants to have to turn their head ninty degrees every time they flick through.
No, not unless the image is licensed for such a use. I the first instance I'd suggest creating your own artwork or licensing some stock images. You may find some 'public domain' images which are suitable.