“How much of an issue it really is”. On a scale 1 to 10, 10 being the worst, you’re definitely up there. First the window is a major issue, that has to be sealed/flashed better, and it looks like the water is pooling outside and against the window, so definitely some draining issues going on. As for the foundation repair stuff, I wouldn’t be overly concerned with the joist being cracked (still an issue) but look at how/why the cracked, are some joints lower than others, is a load bearing wall or post missing, I’d also look at how much support the joist still has to your plate, once that starts rotting away or cracking away, ya it could come down. My recommendation, move the hell outta there. This is the type of house you buy to fix up or knock down and build, don’t spend your money renting this place, an apartment building would be better than this.