For what it's worth (not much) here is my take on uchiko/alcohol. If I use uchiko on a sword in polish I use only high quality uchiko, which I purchased from Bob Benson, the polisher in Hawaii. At sword shows in the States I've heard it called 'polisher's uchiko'. I've never experienced scratching with this uchiko.
That said, I rarely use uchiko on a sword in polish. When I need to wipe my sword I use a micro fiber cloth. I've been told that the National Sword Museum in Tokyo (NBTHK) uses micro fiber in lieu of uchiko.
One thing about micro fiber cloth: new out of the package they have a stitched bound edge. If you're being very careful you'll cut of this stitching, which isn't as soft as the cloth and might trap small particles. The micro fiber can be washed if necessary.
Any alcohol combines readily with water; no matter how pure it will pick up moisture from the air. A friend with a great collection cleans his blades with benzene, if I'm not mistaken. Benzene is toxic; don't know as I'd like to use it.
As to whether a sword needs to be oiled: hard to say. I tend not to but I've been burned before when a small rust spot appeared. I'd try it only if the sword's last polish was at least 6 months ago, if it is in well made shira-saya (so the blade isn't touching the wood), and if the storage area isn't overly humid.
That's what I know. Grey