What is the particular building that representatives and senators meet in Luxembourg?
The number of representatives is currently fixed at 435, even though the population continues to grow. Congress comprises the Senate and the House of Representatives. There are always two senators from each state in congress aka exactly 100 senators. And there are no representatives in Congress, only senators. The representatives are in the House of Representatives.
Each state has a number of electoral votes (electors) equal to the number of Senators and Representatives that particular state is entitled to have in Congress. If a state is entitled to have 10 Representatives and 2 Senators, it gets 12 electoral votes. See Article 2, Section 2 of the US Constitution.