Daang, I should start filling out forms for people for $$$$. Did not know it was this expensive.
If you and fiancé have like 0 issues like former drug abuse, run-ins with the law etc it shouldn't be complicated. Do they provide anything else beside filling out forms for you? I don't think you can take a lawyer for an embassy interview....
If you can read and follow directions and have a bit of attention to detail it is not that hard. Sure it needs some research but this forum basically has it all and you can ask questions. Most of us here did it on our own and we were fine.
"I was told that filling DS160 to schedule interview is really sensitive and needs to be done with precautions." What does this even mean?
What I would do is spend like 3 hours on this forum and in the Guides section some of it might be outdated but in general it gives u an idea of the steps you need to do, then see how you feel about the process, also u can google ds160 form examples (it is an online form so probably harder to practice than just on a simple pdf) then decide if you feel up to it or $1500 worth that you don't have to learn/do it yourself.