On my Greenfield 12-32, the rear wheels are mounted to the hubs by 3 studs and wheel nuts.
The axle also goes through the centre of the wheel rim.
If the wheels have not been removed for some time, they can seem to get stuck in place.
I have in the past just loosened the wheel nuts off and given the wheel a bit of gentle persuasion to get them off.
The wheel hubs are attached to the axle using the spilt clamp method and a woodruff key.
You shouldn't have to remove the hub to get the wheel off.
As for the blade plate, yes it should be flat. If the ends are bent up, you should check for any possible cracks or further damage to the ends.
You could try to straighten them out but my recommendation would be to try a get a good replacement.
The last thing you want is for a blade to come off while the mower is in use.
