Pskov is admin republic - great for trade. You just need to defend from teutons, and have good relations with novgorod.
I think that considering how fast i reached 4 gov tech it shows that kongo is not so very hard.
I have another strategy for kongo. Reach 4 gov tech, and go the colonist NI, then , just wait until you got 1 colonist, and switch to QFNTW, sack all advisors, and mtake a naval and land one. When you got back to 3 stab switch back to colonist NI, and in the meantime regenerate your army, and research area to north, then dow any country and conquer them. Then just continue conquering until africa is yours - and make them all vassals. Then move to maroco, ask them for military acces, then go to algiers, and ask them to, then conquer or ask for acces to tunisia, same with tripoli, and then move to mamluk territory. Ask them for acces, and make your way to some defensless opm. Take them down, take their money, and move thru turkey. Then go to europe, and try to get something in HRE, and then - you know what to do.
It may be hard, but you will get LOT of vassals, and this will bring you great monthly income, and you will be christian. All your vassals pagan. Best if you will be in HRE. Whatever not tried it yet.