Okay lemme see if I can answer your questions.
Wire floors are fine. Some people put fabric/tile over a part of it in case the rats get uncomfortable, but it really is okay if they are wire. It was believed that bumblefoot was caused from wire floors...but now more evidence is pointing to unsanitary conditions, making it more likely to happen with solid floors (urine puddling up on them...).
Yup, 2 is absolutely necessary unless the rat does not tolerate other rats. They become depressed, can develop behavorial problems, etc. without a friend. Besides, you can't be there 24/7 to wrestle, groom, and snuggle with them!
Especially because they are most active at night when we sleep.
There's nothing wrong with feeders...they are usually more skittish and probably not the healthiest, but that's the risk you run with any pet from a pet store, not just those bred for feeders. They can become absolute sweeties, though.
They'll be fine in the same room with the hamster, just don't let them play together.
<--Suebee's mix, always recommended to feed them. Very good for them, much much better than commercial mixes, and rats LOVE it. It only costs about $10 to buy everything, and it lasts a couple months, depending on how many rats you have and how much they eat.