A:AnswerYes, but with the following stipulations: it must be a late 2009 iMac with a 27 inch screen. Target display mode only works with these 2 conditions. Of course you will need the proper usb c to DisplayPort cable as well.
A:AnswerMine does. I run the whole Creative Cloud suite on mine. Works great with all of the Affinity products as well. I have not tried After Effects yet, but will soon.
A:AnswerSimultaneously supports up to two displays:
One display with up to 6K resolution at 60Hz connected via Thunderbolt and one display with up to 4K resolution at 60Hz connected via HDMI 2.0