Let's say it has a 70% effective kill rate. That's okay because much of earth's nuclear armaments are no longer stored in nuclear bunkers (to be explained below), and those bunkers which contain nuclear weapons will tend to be those most well concealed, rather than the most hardened, and thus those most likely to survive this attack.
4. Powerful lasers now aim at the electrical infrastructure. Knocking down power in all cities.
5. Aliens prepare for the next step... full combat invasion.
This part doesn't fit very well with their motivations... Any "sit back and pound" strategy would likely run far against the grain of an alien race spoiling for a fight. But it's okay in the context of this chain of events, as you'll see below.
However, it is anticipated and countered by the dissemination of large generators to sensitive areas, the disguising of electrical power generation facilities and substations (which would begin very soon after initial detection), not to mention other essential facilities such as water treatment, manufacturing plants, military bases, etc. Misdirection tactics would be used to create dummy facilities for the aliens to target, some less essential facilities will be purposefully sacrificed, some essential systems will be hardened against laser strikes, forcing reliance on KEWs to take them out, thus extending their lifespan beyond what would be expected. Since as you said before, the Degravians cannot read English, I'm assuming they can't read French or Dutch or any other earth languages, their ability to determine what function many structures play would be severely hindered, allowing military manufacturing to continue pretty much uninterrupted, barring the occasional lucky strike.
I figure about 25-40% effectiveness in these strikes against the electrical infrastructure, and virtually no effect on military-required infrastructure (which is already hardened against and concealed from aerial or space bombardment).
The (limited) effectiveness of these strikes however will harden the resolve of the defenders. The Degravians have thus eliminated virtually any chance of extracting human intel from any captives, and have turned a scared and awestruck populace into an insurgency waiting to congeal, not to mention ensuring the movement of the earth from a collection of nations at war to a collection of nations in a state of total war. All earth resources are now turned towards defending the planet, putting the Degravians at a significant disadvantage in the long term.
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2. Powerful lasers shoot down anything flying... planes, balloons, etc.
Aaaaaand, here's the kicker...
The defenders would refrain from launching aircraft for the most part, aware of what would happen to them after the limited effectiveness of the initial nuclear assault. Those aircraft launched would use cloud cover and high speeds to avoid destruction. Military combat aircraft would be prepped and hidden in concealed and/or hardened hangers, ready to be deployed the instant any alien aircraft are detected (which would be almost the instant they are launched, thanks to orbital radar facilities). Among them are included many stealth bombers and other high altitude bomber craft armed with air-to-air missiles, retrofitted (given the month of preparation time) to attack orbital targets, so that when the landing craft and their fighter escorts are deployed, there is a convenient smoke screen from which to launch another nuclear assault, this one with far more likelihood of success, given the smaller size of the weapons and the shorter distance traveled by them. Vast numbers of tactical nukes could be launched (just imagine how many tactical nukes could be built by all the world's nations in a month, not to mention all those not used up already), following flyingbuttressman's earlier suggestion of a 'nuclear shotgun' type assault.
Thus, thanks to their overly cautious preparations for the ground invasion, they're facing a conservative 40-70% losses by the time they make a beachhead. Surrender ensues, they trade technology for resources with which to rebuild, and move on to seek a less cunning opponent.
One of the better known precepts of military planning is to never underestimate your opponent and go rushing in without proper preparations. But few people are aware that to overestimate your opponent and spend too much time getting ready can be just as dangerous.
HOWEVER!!! I don't like this ending.
Since I'm sure everyone can agree that you are no space viking (I think, I may be wrong

), we must allow that you would think in more human and practical terms than the leaders of a fanatical warrior cult of an alien species would.
Perhaps you'd like to revise your second stage?
Alternately, we can go over it and my response, piece by piece, but I'm pretty confident about this one.