No, you don't need a lawyer to do the paperwork.
However, if you have realized your case has any of the typical snags that could lead you to appeal (as ours does and I wish I had looked at case law and read people's interview and appeal horrors earlier) then I think a lawyer can be helpful in appraising the quality of your evidence and coaching for interview. We're two weeks to the interview, and I'm still thinking a last minute evaluation of strong points, how to handle things and some critical interview coaching is well worth $1000, if it saves multiple thousands plus a year or more of separation misery or relocation stress and cost during appeal. I found a very experienced immigration lawyer who used to be an IAD judge and is of my husband's ethnicity and has connections to the community, its issues and biases, and the trends at that embassy. Well worth $1000 an something I cannot provide. The kind of well connected friend I do not have, but money can temporarily buy. Still thinking on it.
Is your case complicated at all? Many people here could tell you, as could a search in CANLII for terms spouse genuine and "appeal allowed". The ones where the appeal was allowed shows you where the borderline issues are, the ones the IOs make mistakes on. Presuming that genuine is the typical concern. For other people it is admissibility and so on.