I was always told you shouldn't harvest rhubarb during the first year and then only lightly in the second year. It's an easy one to grow but likes to be fed well.
I have an enourmous bed of rhubarb, and treat it badly, but every year it comes back bigger than before. I don't feed it, just cut off any flowering heads.
i also get two crops, one now and one in the late summer. I would leave them for a while, and see if new shoots appear, then cut he older ones.
You need to do as RS says so that the root system can build up after that it will take any amount of abuse. Feed it in the winter, you can use unrotted compost thrown on top.