I did mine as a 3 step process. I exported my live SMF Database to my local machine, I then ran a WAMP server and emulated my live production into a pre-prod environment. I made any changes I wanted to make there, such as removing custom BBcode and anything else that wasn't going to be transferred over, on this site somewhere, I did post the script I used on my SMF database.
I then automated that script (pasted all of the commands into a notepad document and saved that for bulk usage as a SQL Query.)
I then did several trial runs of converting from SMF to NodeBB to make sure everything went smoothly.
Once I was happy with that, I put my SMF site into maintenance mode, exported the DB. Ran my queries, ran the exporter into the new NodeBB, and as that was happening, changed the nameservers to point to my new server with a custom be back soon message until NodeBB was ready to be started.
I did then have to spend a bit of time going through and making small changes. But the exporter isn't one size fits all, I had a number of custom plugins running.