Disc pads dragging on rotors

Not normal at all. While there's no springs to retract the pistons the "knock back" from the bearing clearance in the hubs should let the rotors be free of the pads if the brakes aren't applied. Either way if you've unbolted the caliper it should slide off, unless something is still holding pressure in the caliper. If there's a grinding noise, then either you've gone metal to metal somewhere on the pads or it could be that you're losing a wheel bearing.

The internally collapsed brake hose is usually the culprit if the issue is only on one side. It can happen with really old or even brand new brake hoses, and you can't tell from the outside. The fluid usually pushes past the collapse when you step on the brakes, but it's enough to hold pressure on the caliper side of the collapse so the brakes drag.

If it's both sides then it's more likely a master cylinder issue, but it could also be an issue with the brake lines above the point where they split.

One sided can also be a caliper piston seal or a piston that's sticking in the bore.

Sliding calipers can also bind up between the caliper and the caliper bracket, but, the pistons should still move freely in that case.