Is frozen broccoli as nutritious as fresh?

Generally yes. It is blanched and frozen soon after picking, so vitamin C holds up better than in fresh broccoli that has spent days in transit and storage.

How do I cook it without it going mushy?

Steam or roast it straight from frozen rather than thawing first. Thawed florets release water and turn soft. Roasting at high heat with oil gives the best texture.

Does it come with stalks?

It is sold as florets, so the thick main stalk is trimmed off. Smaller stems are still attached to the heads.

Is it actually organic?

The product is labeled organic, which means it was grown under organic rules that restrict synthetic pesticides and fertilizers. Look for the USDA Organic seal on the bag.