Given that the people living north of the Wall are basically hunter gatherers in tiaga and tundra biomes its hard to see there being more than about 20 000 of them. Its a bit like the Sami people trying to invade late medieval Holy Roman Empire.
The Others should have nothing close to the numbers to pull it off.
Your tactics for meeting them is surely to maximise your standoff weapons, long bows and cross bows. Get knapping a shed load of obsidian arrow heads for the large contingent of Westerosi bow men. And use the current arrow stocks as fire arrows, you could pull together enough firepower to make it like first day of the Somme for the wights. You are not facing humans with independent thought so the mass infantry tactics do not need to plan on high skills one on one combat. You are wanting a good thick shield wall, no need for a mobile shield for duelling. Something close to the Roman scutum, spike to go into the ground for traction and thick wood. Body length and interlocking. Yer Unsullied are trained to fight Gascari (spelling?) legions so will be familiar with the basics. You will want to make them of solid hard wood and soak it in water for a day or two so it is very damp. Hammer some big nails throw it them attach flammable material to the outside. Their tactic is to wight wave attack at you then overwhelm with numbers on close in grabbing and suffocating. Let that wall of wights storm through the Riverlanders longbows and the rest of the kingdoms crossbows where any hit is a-fire, wights are essentially desiccated fat, BURNS. Then when they begin to mass against the shield wall, get the fires going. The press will means the ones closes have no way out, the water logged shields will take a bit to dry out so will hold back the firewall.
Your formation is
best as a series of squares with shields and
halberds to the outside and bow weapons on the inside with short range throw able firey things for when the press starts. The point of squares is if one has a catastrophic breach you do not lose the whole army, just a division. And it breaks up the attack so you do not have full mass at one point, often they will be between points of the squares so not really able to exert pressure and a greater killing surface area for the same mass of soldiers.
I also have no idea how the hell they are going to hold back a massed attack of heavy cavalry without the
kind of shitron.
Add to all this, Danny and her dragons, they will not be able to come in effective range of the Night King and has light
FlaK. But that is about 500m. Its also about 500m altitude. Given the long bows have a range of 300m, he is going to just about be able to cover his front lines with his magic ice FlaK. But it means any wight force beyond that is getting the full Apocalypse Now. That again compresses their hoards and funnels them into the arrow storms and fighting squares.
None of this will bother the show runners. Or most of the fans.
Random ramblings.