I've never had paella cold. Sounds strange to me, but that doesn't mean it won't or can't be good. Just that I'm not used to it.
Short grain paella rice is much like arborio for risotto. It's very starchy, so if you don't want the rice grains to stick together, don't use short grain. Having said that, if your paella is turning to mush, then it sounds like you might be overcooking it. Mine doesn't turn to mush until the third time reheating. But then again, paella is never really loose. . .
I would suggest to fry the chorizo first, and release the fat and flavor, remove, then add the rice and stir around until pearly. I would add the broth with saffron, then the cooked chorizo after the rice is done. The sure fire way to keep the rice grains from sticking together is add fat - butter or olive oil - when 'pre-cooking' the rice (fry it in the fat). The oil will give it a nice sheen. You could also wash the rice before hand and remove more excess starch, but definitely long grain. EDIT : after consultation, you can still use short grain..: )
I personally wouldn't cook the tomato's with the rice though, just to keep it fresh and clean if you are doing a salad. I'll also say that roasted red peppers might add that additional paella flavor instead of sauteing dice with the onions, although a traditional spanish sofrito includes red or greed bell peppers. . . I'd also go with a sherry or red wine vinegar. Lemon and pimenton (chorizo)/saffron aren't flavor buddies, IMHO.
Anyway, just my two cents.
Edited by jake t buds - 5/14/15 at 6:56pm