Now can we then conclude from the above that Jupiter's Galilean moons will eventually crash into the planet?

It’s certainly possible; it’s also possible that some other subtle effect(s) is/are playing out that will give a different outcome. A large part of the problem is that as soon as you have a gravitating system that consists of three or more

*real* bodies, the system is inherently chaotic in the mathematical sense where the tiniest perturbation can produce vastly different results. The short of it is that I don’t know what the situation is with the Jovian moons.

What I also wonder is how exactly the planets are slowed in their orbits.

As I tried to explain in my second post, the deformation of the bodies changes the mass distribution of the system over time. One way to think about it is that changes in mass distribution affect the inertial relationships between the bodies by introducing small variations in the forces of gravitational attraction between them. Thus, those forces of attraction become briefly and slightly unbalanced and so allow the bodies to move slightly apart or closer together, depending on the nature of the imbalance. Remember that real matter does not react instantaneously to applied forces or stresses; almost invariably, one finds hysteresis, plasticity, elastic and viscosity effects (without which the internal heat generation wouldn’t work, BTW). It is these material properties and effects which cause those small gravitational and inertial imbalances to occur in the first place, as illustrated with the hypothetical case involving perfectly rigid bodies. A reverse situation can be envisaged with a child on a swing who imparts internal energy to the swing with carefully synchronised rhythmic accelerations: the child’s internal energy becomes simple harmonic pendulum motion of increasing amplitude.

Another thing that occurs to me is that in a perfectly circular orbit, there will no longer be any tidal squeezing effect.

This is not quite correct. It will be true in a few special cases, namely (1) the orbiting bodies are point masses; and/or (2) they are perfectly rigid; and/or (3) the bodies rotate around axes perfectly perpendicular to the plane of the orbit and at the same rate as their orbit (that is, the bodies perpetually show one another exactly the same face). Any changes in aspect from one body to another over the period of the orbit means that there will a differential in gravitational potential which changes its relative location in the body. More simply, the back of the body (where the gravitational attraction is at a minimum) eventually moves to the front (where it is at a maximum) and then recedes again to the back. But it is precisely this relative movement of the differential in gravitational potential that produces heat.

What a fascinating place the universe is, when even such a seemingly simple setup has so many subtleties to take note of.

Agreed. Unreservedly so.

'Luthon64