Now can be used at the beginning, middle, or end of a sentence. All sre correct but may sound strange in different contexts. E.g. Now, is it spring? PS ... seasons are not capitalised ... although I have no idea why; some conventions are just random.
I agree that "now" can be used in a lot of different places, but "Is now spring?" just does not work for me. I think the problem might be that it somehow makes it sound like "NOW" is the ONLY time when it's spring.
I would accept "is now spring", "is spring now" as well as either using it.