More than the PS4, so 130M-150M.
I don't understand all those who say 110M or less. There's simply no reason for the Switch to crash like the Wii did, sales are way up and don't look like they will come down anytime soon, so most probably this year's sales will be up from last year. This would put the console already at over 75M, and over 10M more than the Wii had at the end of 2009. The Switch would need to crash even harder than the Wii did just to be able to stay below 110M at that point, and that simply won't happen. The reasons for why the Wii crashed so hard are simply not given for the Switch.
Bonus Question: Just one, though I possibly buy a new one when a more powerful model comes out, giving mine either to my cousin or my wife.
The Nintendo eShop rating Thread: http://gamrconnect.vgchartz.com/thread.php?id=237454