1787
* Northwest Ordinance passes, banning slavery in the US territories (essentially the Northwest) and in all Federal territory acquired in the next ten years [OTL only had first part]
* Constitutional Convention finishes document for ratification [same as OTL, only without clause regarding slave trade]
1790-92
* a bill imposing high tariffs on imported slaves
* NC cedes Tennessee District (as OTL), Georgia cedes the Yazoo lands (earlier than OTL) and, under immense pressure, VA cedes Kentucky County (unlike OTL where they were never a Federal territory)
1792
* Kentucky becomes 15th state, without slavery
* a young Eli Whitney takes a tutoring job in New York [in South Carolina OTL, invents cotton gin]
1795
* Tennesse, following Kentucky's lead, becomes 16th state
1798
* President Adams signs a law banning the importation of slaves to the United States
1804
* following Louisiana Purchase, Jefferson issues an executive order restricting slavery in the territory north of the 33rd Parallel; later withdraws it on constitutional grounds, and as Congress is presenting him with legislation to the same effect
1808
* invention of the Cotton Gin
Now, to reiterate, this means that slavery, when the gin is invented, is only legal in the south coastal states from Maryland to South Carolina and in South Louisiana Territory (LA state OTL). (Also, IIANM, most plantation owners would be former Frenchmen.) Most else is the same or roughly similar to OTL.
President John Adams outlaws slavery in the Louisiana Purchase, based on the precedence of the Northwest Territory.
Yup, not much of a challenge.
All OTL:
On March 1, 1784, in defiance of southern slave society, Jefferson submitted to the Continental Congress the Report of a Plan of Government for the Western Territory. "The provision would have prohibited slavery in all new states carved out of the western territories ceded to the national government established under the Articles of Confederation." Slavery would have been prohibited extensively in both the North and South territories, including what would become Alabama, Mississippi, and Tennessee. His 1784 Ordinance would have prohibited slavery completely by 1800 in all territories. Congress, however, rejected Jefferson's original 1784 Ordinance prohibiting slavery by only one vote, due to an absent representative from New Jersey (who planed to vote in favor but was sick in bed)
POD: Slap some health into the representative and bingo you got no new slave states and southern planters frothing at the mouth.
All OTL:
On March 1, 1784, in defiance of southern slave society, Jefferson submitted to the Continental Congress the Report of a Plan of Government for the Western Territory. "The provision would have prohibited slavery in all new states carved out of the western territories ceded to the national government established under the Articles of Confederation." Slavery would have been prohibited extensively in both the North and South territories, including what would become Alabama, Mississippi, and Tennessee. His 1784 Ordinance would have prohibited slavery completely by 1800 in all territories. Congress, however, rejected Jefferson's original 1784 Ordinance prohibiting slavery by only one vote, due to an absent representative from New Jersey (who planed to vote in favor but was sick in bed)
POD: Slap some health into the representative and bingo you got no new slave states and southern planters frothing at the mouth.
Is Kentucky part of the deal, or was it considered as simply part of the 800-pound gorilla, Virginia?
Kentucky was never a Territory, so isn't affected. It stayed part of VA until ready for statehood.
OTL, Tennessee was briefly a Territory, but TTL probably wouldn't be - just stay part of NC until admitted.
In fact, in 1784 the US had no Territories south of the Ohio River. Most of AL and MS remained part of GA until 1802, and would probably remain so a good deal longer in this situation.
Then, it would be likely that under these circumstances Tennessee would remain part of NC, while Alabama and Mississippi would part of Georgia. Slavery would still be legal, and profitable, in these lands but there would be no new slave states.
This rule might make a difference in a border area like MO, but further down slavery is a bit too profitable for a scrap of paper to be allowed to bar it. Note that the Convention denied Congress the right even to abolish the African slave trade before 1808, so you can guess what the chances are for an outright ban on slavery itself.
If slavery is not allowed in Alabama and Mississippi then you'll not have a need for any imported slaves (which the USA did.
Your likely going to get something like this with Virginia, North/South Carolina and Georgia as Slave States and the rest admitted as Free.