Why is the Blood-Starved Beast stronger than a not blood-starved beast?

Because hunger forces animals to use desperate measures in order to survive. Like they take more risks and think less about the danger of their actions, getting food is the absolute top priority. I guess.

Why does hitting someone with a cane twice do more damage than shooting them seven times?

Because at low bloodtinge you basically shoot slightly-blood-infused peas.

Translated in Japanese, Rom the Vacuous Spider translates to Rom the Stupid Spider. Why is she stupid? What is used to measure the intelligence of a spider from space?

Serious answer here. Rom was once a scholar of Byrgenwerth but was granted eyes on the inside by the Great One Kos. Because of that Rom ascended to something similar to a Great One herself but lost her mind in the process.

Why is a newborn infant such a skilled fighter?

Survival instinct. He's not fighting in a very efficient manner, it's more like he's constantly flailing around wildly.

What exactly is keeping Gherman from leaving the Hunter's Dream?

He's probably bound by the Moon Presence, like you are when you kill Gehrman but haven't eaten three baby strings.

Are people actually buried under the headstones in Hunters Dream/Hunters Workshop? If so, whose headstone reads "All the places in Yharnam you can go to"?

Supposedly they belong to other hunters who went through the same thing as the player. It's assumed that Eileen and Djura also have graves there.

The pebbles are petrified eyes, and the Barking Crows drop pebbles because they eat eyes. If a Barking Crow eats enough eyes, can it ascend?

I'm not sure if pebbles are actually petrified eyeballs. I always just assumed they are stones that were carved into shape. Crows drop them because birds actually use stones to digest their food (or something like that)