Car radio wiring with heat shrink tube only it is good ?

If you mean joining wiring solely by using heatshrink, no, that is nowhere near good enough. Heathshrink is used to protect proper joints AFTER they have been made.

Not as good as soldered wires. There is a mechanical connection, but it can be negatively affected by stress and corrosion. A cold joint, or crimp union may work the same, but not insulate the way shrink tube does.

Good luck: I don't think a "twisted wire" connection will last.

There's too much vibration and environmental temperature changes for a stable joint.

You don't have to solder, though.  Check out the variety of crimp-on connectors and splices.  For most, all you need is a pair of pliers (no special tool).

No.
Heat shrink tubing is only for insulation.
It does nothing to keep wires connected to each other.

I would think so!