Now, on the issue of the Senate...it was also designed as a sop to the slave states, due to the population issue mentioned in the Madison quote here. The North's preponderance in voting-eligible population meant that it would inevitably dominate any legislature which was properly "democratic," ie, one which gave equal representation to people on a one-person, one-vote basis. The Senate meant that rather than having to outweigh the North massively in population so that they could hold their own in the House of Representatives with the right to vote restricted to a smaller subset of white men, all the slave states would need to do was ensure at minimum, an equal number of slave and free states to ensure that their power in the Senate could forever veto any Northern attempts to limit or abolish slavery.