My family and I moved to Spain in 2016, under a non-lucrative visa. We used an immigration lawyer to help in this process. After some time, I considered whether or not I could have done it on my own, and the answer was "yes".
What the lawyer did for us, and my comments on whether we could have done this ourselves:
1) Pointed us to the correct forms. This is actually fairly well explained on government sites, and from others who have undergone the same procedure
2) Setting up a bank account, in Spain. I haven't really looked into this but I think that this is something one could easily do while on a visit to Spain; which may be necessary in order to overcome the proof of residency requirement (see below)
3) Obtain NIE. Everything I've heard, although I haven't done it, is that this can be easily done, oneself, with an appliction in country being the easiest. Again, another reason for a visit.
The next item below, satisfying proof of residency, was something we did on our own with no contribution from the lawyer
Establishing residencey (rental contract):
For me, the most problematic part of the process is that they require proof of residency, ie, a rental contract, as part of the application. The money spent on rent from the time of signing, to the time of visa granting, was 5 months for us. That was wasted money, from my perspective. But I was ok doing it, considering it just a "cost of getting a visa".
When we were thinking about moving to Spain, a family friend recommended Valencia to us; she went to University in Castellon de la Plana. So, we made a short trip there to confirm that it was all she said. While on that trip, we rented an apartment.
In retrospect, as Spanish leases have only a six month minimum, I would have leased the absolute cheapest place I could have found, and then once we arrived, canceled that lease and found someplace more to our liking. I would have saved quite a bit.
Maybe others in the forum know of other workarounds, like a long term lease on an Air BnB that would satisfy the residency requirment.
In retrospect, I don't regret using the lawyer, as they helped lower the stress of the process. Primarily by answering questions about how to do things, and take care of the NIE and setting up of bank account. But I think that, with a bit more research, one could do those things themselves.
Regards and good luck on your move