Seems okay to me.
Since the consensus seems to be that our ukes like as close to 50%RH as possible, anything over would help to add moisture to your instrument; however, if your cases/containers are air tight, a bowl of water inside the container can quickly get the RH (relative humidity) up towards 100%... besides the issues of wood warping and metal rusting, over 80% invites mold growth and wood quickly starts to rot away at over 90%RH... and that might not be good for your uke.
I would use those hygrometers to see what the RH is in there... and take out the bowl of water when it gets too high... of course if your uke hasen't completely equalized yet it will continue to absorb the humidity in the container and the RH will go down until equilibrium is reached. you can reintroduce the bowl of water to raise RH and repeat till the RH in the container stays near 50% with only the instrument in there. Theoretically, if the container is air tight, and the uke has been equalized to a particular %RH (say 50%), then you should be able to maintain that RH in the container indefinitely.
If you are looking for a less finicky solution, you can get better control of the humidity levels with cigar humidor products... adding a humectant like propylene glycol to your bowl of water can help to maintain a certain level. 50/50 propylene glycol and water solutions commonly used for cigar storage might be okay, but cigars are stored at higher RH (60-75%) so in an air tight container 50/50 might not be ideal... a different mix of propylene glycol and water might work better.
There is also a product that cigar peeps call "beads". Its manufactured by a company called Heartfelt Industries and , like the propylene glycol and water solutions, also tries to keeps RH at a predetermined level. you just spray/mist distilled water onto the "beads" and they will release or absorb water as needed to keep RH at the set level. "Beads" are available in RH levels as low as 60% which might be good enough for ukes.
Personally I use a product called Boveda Humidity Packs (also a cigar world product) which are pretty cheap and maintain RH at a set level and are available as low as 65%RH... which hold RH in my less-than-air tight cases at between 45-60% depending on the case. They are not supposed to be reusable but when they dry out I just throw them in a air tight container with a lot of distilled water (not touching the pack) and the very high RH inside the container rehydrates the packs effectively making them reusable.
as for the sharp frets, if re-humidifying your uke doesn't work... a file will... get someone that knows what they are doing to file them down. I find that a lot of times, especially on vintage ukes, re-humidifying is not enough.
good luck!