The title tune appears to be about Largo at first. The lyrics mostly match his character and most of the Bond songs are about the villains, including the previous one. But on a closer analysis, the lyrics point to it not being about Largo, but about Bond himself (his fight goes on and on and on, any women he wants he'll get).
As noted on the Headscratchers page, the Aston Martin's water cannons seem pretty useless. However, they actually make for a potent weapon. A highly pressurized stream of water sprayed at a pursuing vehicle's tires would easily shred the rubber, or create a film of water on the road surface, causing the pursuing vehicle to hydroplane, or spin out of control. The water would then evaporate, leaving no trace for investigation.
In the intro, Bond kills a villain played by Bob Simmons, a stuntman who played Bond in the gunbarrel sequence; this film was the first to feature Sean Connery in the gunbarrel.
When the imposter demands more money from SPECTRE it sure seems like a case of Too Dumb to Live. But he may have just been Genre Savvy enough to realize that he is a massive loose end for SPECTRE and that they will almost certainly try to get rid of him the moment he has outlived his usefulness so even though he came across like a Smug Snake it’s possible he realized he needed a much larger amount to ensure he could disappear.
Largo tortures Domino when he finds out she was helping Bond. If Paula hadn't taken cyanide, he would have done the same to her.
The Disco Volantewas carrying a nuclear missile when it exploded. The massive explosion probably generated deadly radiation and spread radioactive debris. The whole area must be contaminated, and at the very least James Bond, Domino and Kutze were irradiated.
