Short answers, pulled from the story.
The fourth and current Winter Palace was built and altered almost continuously between the late 1730s and 1837. The Italian architect Bartolomeo Rastrelli (1700-1771) was its principal designer, creating the present building in the Elizabethan Baroque style at a final cost of 2,500,000 rubles.
The Winter Palace is said to contain 1,500 rooms, along with 1,945 windows, 1,886 doors, and 117 staircases. The total floor area is 233,345 square metres across a site of 14.2 hectares.
On the 25th of October 1917, Bolshevik forces including the cruiser Aurora bombarded the palace from the Neva while capturing the Peter and Paul Fortress. The Provisional Government under Alexander Kerensky was arrested in the Small Dining Room by 2:00 am. The Bolsheviks actually entered through a back door left open by wounded and disabled guards.
The Winter Palace and its surrounding buildings now house the Hermitage Museum, one of the world's largest art museums. The palace was declared part of the Hermitage public museums on the 30th of October 1917 and today attracts an annual 3.5 million visitors.
Empress Elizabeth commissioned the present palace in 1753 through architect Rastrelli. Catherine the Great (reigned 1762-1796) assembled the Hermitage art collection and added three major extensions. Nicholas I oversaw the complete rebuilding following the fire of 1837. The palace served as the official imperial residence from 1732 to 1917.
The cause of the 1837 fire was unknown, but its spread was blamed on architect Auguste de Montferrand. Pressed by the Tsar for a fast completion, he had used wooden materials where stone was required. Disused fireplaces hidden behind wooden partition walls acted as flues, allowing the fire to travel undetected between rooms. The blaze burned for several days and destroyed most of the interior.