Lincoln"s early career articulated the abolitionist movement very clearly, when they did 2 hour long speeches he spent hours discussing it. When he was elected, his hope was to resolve the problem legislatively and that all changed when the south seceeded. That's when he was faced with the priorities you describe.
It wasn't the first time, in order to even have a United States there were several compromises during the Constitutional Convention, the most demonized being the 3/5ths compromise. Agitators try to say the founders were sooooooo racist calling an african only 3/5ths of a man. All it takes is to read it and the history.
Regarding the census and appropriation of congressional representation, the south wanted slaves to count as full citizens. The north didn't want them counted at all so that legislatively they had the numbers to end slavery. If the north had not proposed and the south accepted that slaves would be counted as 3/5ths of a citizen (not a human being), the south would not have joined the union and there would have been two nations, one slave and one free sharing the continent. The north knew they would eventually outgrow the agrarian south and could end slavery. As Lincoln said at Gettysburg- four score and seven years.
Escaped and free former slave Frederick Douglas, after his anger over his enslavement had subsided, said that the 3/5th compromise was the most brilliant thing done by the founders, it guaranteed an end to slavery.
And sadly everything is considered racist today.