The Electoral College then (and now) gives each state a number of Electoral Votes equal to its representation in Congress. In essence, every state receives two votes (Senators) plus its House delegation's size.
Iowa has four seats in the House... plus the two Senators... equals six. This has had the (to me, beneficial) political effects of slightly increasing the power of small, rural states in presidential elections (only slightly, though, certainly not as much as the Senate does) and making the election about competitive "swing states." This, again, to me, has the benefit of demanding presidential candidates attempt to appeal to a wider geographical and socioeconomic coalition than if they could just camp on the major cities going for the popular vote freely ignoring large regions of the country.
The involvement of the noxious three-fifths compromise with the Electoral College is indirect. The main issue with the three-fifths compromise was if Mid-Atlantic and Southern slaves states could count their slave population towards the population used in their Congressional apportionment. When some states had more slaves than free people (e.g., South Carolina was 43% slaves in 1790 and 57% slaves in 1860), how much weight their slave populations would have in the Congressional apportionment would have a lot of influence on their voting power in Congress.
The Electoral College was just downstream of that. Not saying the president was an afterthought at the constitutional convention (though the office of vice president certainly was), but the real debates in framing the new government were over Article I and Congress. Congress was presumed to have had most of the power at that point in history -- the president was there in many ways just to "mind the shop" while Congress was out of session.
The convention did not put nearly as much time into Article II as Article I. The debates around Article I, such as the Connecticut compromise and the three-fifths compromise and the compromise that protected the slave trade until 1808 from regulation by Congress, were the ones that took much most of the oxygen.
The Founders certainly did not imagine a future where governing was so executive-heavy and the president was at the center of American political (and even social and cultural) life like the office has become.
So no, the three-fifths compromise was not "part of the original Electoral College." It was part of the original formula for determining the apportionment of House seats, which has a downstream effect on EC votes.
