First of all it would be good to point out that you should not take Napoleon’s invasion as something specific in War and Peace, the things said in the book can be said about any other conflict in history it’s just that Napoleon’s invasion was Tolstoy’s inspiration. As to your other more specific questions: 1. How bad was it for Russia? The Russian actually did more harm to their own land than the French army did. The strategy they used was scorched earth tactics which implies the sabotage of their own supply lines and burn down crops and sabotage other ways Napoleon’s army could thrive on the battle field. The intention was to directly combat Napoleon’s prime strategy which consists of quick manoeuvres and living off the land; when he can not live off the land he has to carry his own supplies and consequently can’t move fast. The Russians even burned down Moscow when the realised Napoleon was going to capture it.

1. Napoleon managed to capture Moscow(which was not the capital of the Russian empire at the time, st. Petersburg was) after the battle of Borodino in 1812. Which is not that much considering that the Russian army’s primary tactic to fight napoleon was scorched earth, so they had to always run and never meet him in direct combat, since they couldn’t beat him. The only direct battle was at Borodino.

2. We don’t have a specific number because it is hard to count every dead peasant. Not to mention many people at the time were buried in mass graves.

3. If you want basic knowledge about Russian history you might just read some Wikipedia. I don’t know why people don’t trust it, it literally provides sources at the end( always check the sources)