I'm guessing these two issues are the same as old iMac G5s.
To remove the back, you place the iMac G5 (unplugged and powered down) face down on a flat surface, like a table or desk. Lift the foot so it's as far away from the iMac's body as possible. Peer at the bottom edge of the iMac. There will be 3 captive screws (one left, one centre, one right). There will also be an ambient light sensor to beside the centre screwdon't confuse the two! Trying to unscrew the ambient light sensor is not smart!
Use a Philips screwdriver to loosen the captive screws until they resist. Do not apply excessive torque, or you'll either damage the grooves, or worse, break the captivity and the screw will fall out.
Once the three screws are loosened, grab the area where the aluminum stand goes into the back of the iMac. Lift up and forward (so the bottom comes up), then pull the entire cover backwards and up.
Taking the stand off:
I had to do this when I relocated my iMac from Canada to Shanghai.
With the back cover off, this is how you remove the aluminum foot:
1. Place the aluminum foot between your legs, with the inside of the cover facing you, so that the back of the iMac's cover rests on your thighs.
2. In the centre of the inside of the back panel will be a rectangular, convex shaped piece of aluminum. On either side will be two screws. Use a No. 8 Torx (magnetic is a good choice here, these screws are miniscule) screwdriver to remove the four screws.
3. Remove the rectangular convex cover. Underneath you will see the other end of the aluminum foot, resting on top of the hinge. On the top edge there will be (if my memory serves me correctly) four No. 8 Torx screws, each about three quarters of an inch long, firmly holding the stand against the hinge. Unscrew these.
4. Removing the stand is a bit tricky. First you have to move the upwards because there are two pegs sticking out of the hinge and into corresponding holes in the stand. Wiggle it around until the pegs are no longer in the holes, then slide it backwards out of the slot in the back of the cover.
5. For travel, screw the three-quarter-inch screws halfway back into the hinge. Put the back cover back on the iMac, and cover the exposed slot with tape. I used a large laptop back to transport the iMac, but you can transport it however way you please.
6. Oh, and make sure you put the aluminum foot in checked baggage if you fly like I did. It can be considered a weapon if carried onboard.
Hope that helps.