In my personal experience, having that many animals is challenging but the burden is lessened if the cats like each other. If you can throw some money at the issue (which I understand nobody can) those litter robot things are a miracle for consolidating how many boxes you need and how often you have to tend to them. Room fans and HEPA filters can cut down on smell and the fur problem. Aside from that, it sounds like playing caretaker is probably the primary stress inducer, you just can't do anything immediate about that obviously. Make sure you and your partner's communication is in a good place and just know you'll adapt eventually. How much space you working with?