Yo!
Before I answer anything I gotta point out that I've never been that good with digital stuff, I just kind of get by with methods that might not work for everyone else, you should probably look up tutorials on youtube or other sites as well just in case. But I'll try and answer each question as well as I can.
1. As far as I know Epson and Canon brand scanners are the most recommended for artwork. I have a Canon, though it's not really an optimal model, just something I happened to have already when I started. Make sure it's the right size, A3 if you wanna draw bigger drawings, if not then A4 is fine. There's more info online if you just look up "best scanner for drawings" or something.
For settings: Black and white setting for colourless drawings, a youtube video made by a professional recommended 1200 DPI but my scanner only goes up to 600.
When scanning coloured drawings you wanna turn the contrast to max for the best lighting.
As far as double pages go I just kind of stuck the two images together as precisely as I could, there WAS a little seem left initially but I got rid of it on my art program, pretty much just by zooming in really close and filling in the blanks. If there's a tutorial for a better way to do it I haven't found it yet.
2. I have a Wacom Intuos tablet (small size). It doesn't have a screen built into it cause those are really expensive, but it didn't take me that long to learn to use it even if I had to look at my computer instead of my hand while drawing. Wacom Cintiq has a screen.
3. I have Mangastudio 5, but Photoshop is perfectly fine too (possibly better), I've heard Paint Tool Sai works too.
4. Most likely not just because it really isn't something I specialize in, there should be plenty of tutorials for Mangastudio and Photoshop on Youtube that are better than what I would put out.
Sorry I can't really give manual level answers, hope I can still be of some help.