Very few. Most Republicans, including Lincoln, were not abolitionists. They opposed slavery but did not demand abolition. They only sought to contain it where it existed. They were "Free Soilers".
Well considering tariffs had been on the forefront of national discord for over 40 years and the fact that slavery wasn't even broached by the Whig/Republicans seriously until the mid 1850s
Tariffs had not been a political issue for decades by 1860. That issue was resolved in 1833 and tariffs decreased every year afterward and were at their lowest level ever in 1860. Slavery became an issue in the 1850s because the slave powers pushed through the Kansas-Nebraska Act, which overturned the Missouri Compromise of 1820. It was followed by the Fugitive Slave Act, which trampled both states-rights, and individual rights and drove further wedges between the sections. It was again more 'in-your-face' overreaching by the slave powers. Those bills killed the ever-compromising Whigs as a national party and the free states reacted by creating the Republican party and it's free-soil platform. The Republicans would have never come into existence if the slave powers had not dominated the Democrat party and discarded all previous compromises.
The south, or more correctly, the Slaveocracy of the south who controlled all political power, made slavery an issue, not the north.
Not true. The issue emerged in the wake of the 1857-59 recession, which economists tend to blame on world financial disruptions caused in the wake of the Crimean war, but which protectionists at the time blamed on low tariff prices.
By 1860 the protectionists were advancing new tariffs in Congress with full force. By May the House had passed the Morrill Act on a strictly sectional vote. The GOP platform adopted protectionism as a major plank and their candidate, The Lincoln, advocated a new tariff hike, all of this before a single state seceded.