1.) What size do you use for your pixel art? - I use a canvas of about 250x400 -w/h- (for the most part)
2.) What program do you use? - Paint tool sai, more specifically the Binary pen.
3.) Do you use a tablet? - Yes, I do. I have Wacom: Bamboo Fun Small.
4.) How long does your pixel art take? - Anywhere from 3-5 hours. It can be longer but it depends on the detail that needs to be added.
5.) How do you make your backgrounds transparent? - GIMP. It's a free program so google it. When I use GIMP I open up the file and select the white background that I don't want with the magic wand tool (with pixel art I can use a threshold of about 15% but for traditional anywhere between 35-70% will be enough to clear the white as long as your lines don't have gaps in them) - Afterwards go to the layer option and - add alpha channel. Then simply press delete (making sure your white background is still highlighted with the magic wand tool.) and Presto! You have a transparent background. Then make sure you save with an extension file of .PNG.
6.) How long did it take you to learn? - I started doing Pixel art when I was about 12, by making and editing sprites on MS Paint where I got a grasp of how to do pixel art, I then mostly did icons until I started experimenting with bigger sized canvases a few months ago.
If you have a question feel free to ask and I will answer it here~