Caucasus Provinces OK, but Kiev Threatened

Although my strategy of protecting my southern Russian provinces has worked so far - the Georgians and their mates from Dagestan have been pretty cautious about attacking, I made the mistake of moving my Southern field army to the Don to support these provinces. The sneeky Crimean cossacks then decided to go across the border and rampage through the Ukraine, eventually taking Kiev.

I sent my field army off in pursuit, but not before they managed to assault and take the town. It's amazing how confident the AI is when it comes to city assaults - they always just go for it rather than settling down to a long siege, even if the odds are pretty much 1:1. Luckily they seem much more cautious if you have walls - as I do in my southern provinces.

I have now retaken Kiev, but the bloody Swedes are acting up now and have declared war. So I have a dilemma - who do I actively fight - the Crimean Khanate, or Sweden? I can only really afford a decent army in one theatre of war. So far I have sent a couple of regiments of line infantry to support the northern field army in case we are invaded from Ingria. However, there are still a number of active Crimean forces in the south who I would ideally like to deal with, but that might leave Kiev vulnerable again unless I raise more troops.