Last update on this bass.
I have added a string retainer bar at the headstock to press the strings down over the nut, I have made new string grooves in the nut (on the sides I had to make them almost 2mm deeper than they were originally), I have polished the fingerboard, I have made string guide grooves from the tuner holes to avoid string breakage, I've added rubber pads under the stand mount to avoid too much sound from going through, I have sanded the back of the neck to make it more even, and I've made new string grooves in the bridge and installed a new Fishman BP100 pickup system on it.
The builder sent me another piece of crap mic for installation under the bridge of the bass, but as you guessed... it's not very usable. It probably works, but the wires are too short to connect easily, the finishing is very uneven and the bridge wouldn't have sat straight on it.
So I ordered a trusted Fishman BP100 and have now made myself a bridge sandwich using some spacer bars from a Roland GK3 pickup that I had and some double sided tape and the original bridge.
The bass is now playable, except from a smaller section of the fingerboard on the treble side (1-5th position) that buzzes a lot. The rest of the bass is however now playable. It sounds decent, too. The Fishman mic system works great, and I have now basically a "Kydd clone" bass. It sounds like a "cross-over" between an upright and a fretless with flats. It's ok, not quite the uprightish sound I had hoped for, but not totally useless either.
Given the total final price and everything, I'm still at 2/3 of the price of a second hand Kydd.... but the workmanship is probably way inferior to the Kydd. And if you count in the hours spent... I'd say definitely not worth it.
So my advice is... save yourself the trouble, just go get a Kydd if a Kydd is what you want.
If it looks like a turd, smells like a turd, it most likely is a turd.
Hopefully my bad experience with this builder and this instrument will save someone the disappointment in the future.