Go tubeless with used tires I have some tubeless ready wheels and tires, but they were delivered mounted with tubes the old fashion way. I’ve been riding like that for more than 800km, and I wonder if there is a problem removing the tube and add some sealant after so long. Especially since I had a puncture from a small nail, meaning the rubber from the tire already suffered a small punch.
Riding with tubes doesn't necessarily affect the tires ability to hold air without one. In fact, I find it easier to inflate tubeless set-ups where the tire has already seen some use, as the carcass gets a bit more flexible.

That being said, any and all holes in the tire need to be sealed. You may have caused some small ones all around the surface of the tire, but those should easily be handled by the sealant. Depending on the exact size if the nail-induced hole you mention, sealant just might take care of that too. If not, it can still be repaired with a dab of superglue, preferably applied to the inside of the tire.

If you happen to have suitable glue easily available, I totally recommend using it before adding sealant, as it has a tendency to make things messier and glue less likely to stick well.