OK, I would say the glue used if it's like mine is very tenacious, all of it will have to be scrapped off.
The water lapping sound is what it is, but with cabin walls smooth and hard, I think the noise will get some amplification instead of deadening from the rug like liner. Just something to be prepared for.
Other members have done this, just have to wait for a reply - then ask about the sound level change.
You may be better served with a textured or dot vinyl roll material reapplied, I think the OEM surface even when painted will have a very unfinished commercial (Proline Lite style) look, if that's OK with you.
You will still get the mildew, just be easier to get off, either painted or vinyl. I get mildew even on glass and Formica covered wood, no hiding from it.
Windows and doors shut, keeping a incandescent light bulb on in the cabin will avoid mildew, as long as access to shore power is available.