Why can't I go though the crater left behind by a nuke?

The craters created by this mod now have 3 sections (when fired on land):
- The crater rim, which is higher than the surrounding ground, it can be deconstructed by drones, or by hand, like concrete or any other remove-able tile.
It should be noted that the rim should be easily vissable above the terrain, but this is relatively fragile, as tile transitions are hard...
- The crater pit, which is lower than the surrounding ground, and will fill with water slowly, the shallower parts of this are traversable, but the deeper parts are not. This can be filled in with landfill (before or after it fills with water).
- The fireball (not really part of the crater, but still) in this area, all water is vaporised by the detonation, but the area left behind can be landfilled, as if it were still water.

Why does the game crash when I have the Alien Biomes, Asphalt Roads, Dectorio or other tile-heavy mods installed?

Factorio has a hard-coded limit on the number of types of tile in the game. This mod adds about 7 new tiles, which is normally no problem, but the mods mentioned above (and I'm sure several others which add many new tiles) make the game very short on tiles.
To fix this, both of the above mods have options to disable some of their tiles - most prominently, the "Remove Obsolete Tiles" option on Alien Biomes.
Some combination of these settings can almost always resolve the issue.
True-Nukes no longer supports such settings, as it required an entire separate detonation system.

Why won't the nuclear tests work?

You need to select the research, click 'start research', and exit the technology menu.
This can be done before or after detonating the nuke - its just important to ensure that the technology is being researched at some point after the weapon goes off.

How do I set off the 100kt nuclear test?

Make the 15kt+ warhead, the fusion test building, and the required 2 tritium.
Place the fusion building down, and select the 100kt detonation (the one with the standard 15kt+ core).
Put the tritium and warhead into the building, and run a very long way away.

Why are there so many weapons added? Aren't some of them pointless?

Yes, the mod adds loads of weapons, many of which are absurd and seem unusable.
Some of these (like the magazine ammo and the bigger rockets) do have definite use-cases, though require good armor and care to use.
Some of them have little vanilla use.
I prefer to provide the player with a wide range of options, and let them decide which are bad ones. Not all the options are useful in vanilla, but I want to enable ingenuity, and some mods might make other options far more useful, e.g. by adding more armor, longer range weapons, certain types of vehicle, or whatever else.
I also want to create circumstances where people can look at the absurdity of a weapon or system, and try and use it as a challenge, or use it as a joke. The mod already takes things to extremes in so many ways, it feels only right to cover all the boundaries like that.