NBD: Squier VM fretless Jazz

Congrats!
Many people like a very low action with little relief on fretless. It helps get the "mwah" sound that is often desired by fretless players.
If you desire more of a double bass sound then you might try raising the action and maybe even add a piece of foam under the strings near the bridge to mute them.

 

Aren't the RS66s round wound? Unusual choice for a fretless. It's not unheard of but it can dig into the fretboard and wear it. I also like fretless for the Bwow sound it makes.

As for the action, I like it low enough to make it Bwow but not so low that it doesn't play every note clean.

FYI, the truss rod issue is fairly common. Your fix should last a lifetime.

 

Bring up both volumes to full and tone wide open. Back off the volume of the front pickup about a quarter turn. Adjust the tone as need to take out a bit of the high end zing of the round wounds. PLace your plucking hand back by the bridge, use the back pickup as your thumb rest position, adjust accordingly. That is pretty much the starting point for the "Jaco Sound".

 

One other thing, don't scoop your mids on your amp.

 

I find my fretless sounds much better without the mids scooped--but then I also like mids...

 

My fretless has an ebanol board as well. I bought the neck used and the first owner had used rounds. It has some wear from the rounds but not serious. I'm not sure how much he played. He had replaced the neck because he said he couldn't get used to playing fretless.

If you want that Bwow tone, flats will bring that out more. Lower the action until you get the tone you want but it still plays clean. The sign that the action is too low is that some notes don't sustain. Since there's no frets to rattle against, it's when the string lays down on the board that kills tone and sustain. At least that's my experience.

I found it next to impossible to get the tone I wanted with rounds. Between that and the sleeve noise when sliding up and down to and from notes I went to flats. But whatever floats your boat.

 

Round wounds are the choice for fretless. I've used them on my fretless basses for years with no problems.

 

Be aware that if you do switch from rounds to flats, the difference in tension will require some major neck adjustments because the Squier VM necks don't have the carbon fiber reinforcement. I learned this the hard way. The flats were fun to play (much like playing a DB), but I didn't dig the sound. Went back to rounds (and readjusted the neck).