No, you do not need the help of agency to write your sop. Prefer not to.
You should start on your sop pretty early as it really does take time. Mine took a month and my final draft is vastly different from the first. You kinda evolve while you write it, getting better by the day. So just start with it, gradually you will come up with points to add, and shape it up well.
You can ask some elders to proof read it and yes this parts important too. My aunt made me remould like 50 words because they sounded negative to her and i have to concede that she was right. An adult will provide you with a perspective you yourself may overlook.
Lors are a different matter entirely. Dont try to write them yourself would be my advise. Just provide your recommenders with some points that you may want to be included if they are ready to oblige and let them frame it themselves.
Hope it helps.