You can definitely do step 4 on your own. I tried several times and did not get through it. What's worked for me is a "step group." Several of us that started AlAnon about the same time go out for coffee together after the meeting. We each bought the Blueprint for progress workbook. Our goal was originally to do one section a week - each answering the questions on our own as best we can, and then getting together to talk about it. Sometimes we share personal insights we've learned, sometimes we talk about what the questions mean, and sometimes we just talk about what's on our minds.
I'm learning alot about myself, and when we're done, I'll be able to take my step 4 and share it with my sponsor in step 5.
Whether you do it on your own, or with others, I'd recommend the Blueprint for Progress workbook.