How does the SD card reader work?

I can only answer #1 : you have to select the photos/videos you want to import. I believe there is an "import all" button which can be used as well. I don't have experience with the other things you asked.

 

RAW files edited in photoshop save as jpeg in camera roll then got to cloud.

Never done video so cant answer that.

Yours a Nikon user. FWIW the edits are great. I fooled a fellow photographer with one RAW to jpeg image edited on iPad Pro 12.9 & the same image edited on Lightroom 6 on my Mac. The Pro tog couldn't tell which was which.

 

1. Once you plug your SD card in, you get a choice to import all photos or only the ones you select. You can only see thumbnails at this point, so I import all, then delete the turkeys.

2. RAW and video get transferred.

3. If you have a cloud service or Photostream activated, copies are put into those services and you can see photos on other devices. This applies to JPGs; videos do not go to the cloud. Not sure about RAWs.

4. Idk

Keep in mind, the iPad is made to work best with JPGs. RAWs have been problematic from the beginning and still are. On my Canons, I have 2 card slots and shoot RAWs to a CF card, and duplicate JPGs to an SD card. I transfer only the JPGs to the iPad for sharing and light edits, saving the Raw copies until I get home and work on my Mac. RAWs take up a lot of space and will fill up your iPad memory quickly. You might want to shoot RAW+Jpg and import only the JPGs to save space.