Playing on late era:
I actually found that the best thing to do after seizing those rebel provinces in Scandinavia is to go on a crusade before taking on Denmark. Stay on good terms with the pope and after a while, request a crusade to the holy land. Yes, I know Vilinus would be the logical target for a Norwegian crusade, but. The best use of crusades is not to take the designated settlement so quickly. Crusading armies are without expenses, they move quicker and can be used to boost your economy better than anything else. As Norway I managed to get the pope to declare a crusade on Cairo. I held the following regions at the time: Norway+ Uppsala, Stockholm and Visby. While Vilnius was not on the target I destroyed the Lithuanian faction en route to the holy land with the crusading army (using a spy with nearly max subterfuge that travelled with the crusading army to open gates). Once through Byzantine lands and into Turkey I made war with Turkey, quickly seizing, sacking, deleting every building and leaving the province for another one. Iconium alone gives you plenty of cash. I then moved on through Turkish lands, destroying everything in my path before moving on towards Turkey. I think I earned the total sum of nearly 150.000 florins on the crusade, decimating the Muslim powers. With the army I had priests, spies and diplomats travelling along. In addition after making my first 25000(ca.) florins when sacking Iconium I offered Denmark 20000 for Skara and they accepted. Later on I bought Helsinki from Novgorod with crusading money, they gave it for as little as 8000. The regions I sacked and ruined I gave away to establish good relationships with big powers across western europe. And of course, I had to help out the Kingdom of Jerusalem as well.
When I finally captured Cairo my total sum of cash was around 100.000 florins, I had let the homeland grow with low tax rates and had built plenty of economic buildings. At the same time, I had a massive army just waiting to enter Denmark.
This was on VH/VH. Crusades is what gives the catholic faction a huge advantage over the others. The only disadvantage is that the catholic factions always have to be careful about attacking their catholic neighbours, because the relationship with the pope is probably the most important one you have in the game.