1. We book as soon as possible, but one cruise 22months out couldn’t get an accessible balcony.
2. All the lines I have been on I’d rate pretty much equal on general accessibility though some ships are better than others. Queen Mary (I think that was 5he ship) had a few floors that had sections with pretty steep slopes, another ship had lots of changes in flooring carpet to tile to inlay with edges around them (each change caused, what many would consider minor, bumps that caused my back to jar and increased pain. One older ship had a ridge at the fire doors that was difficult to negotiate alone either with poor balance or a Manuel chair.
3. no, save to add you can’t get say a Guarantee Accessible Mini Suite, which may cost less than picking your cabin. I have never seen a line with guarantee accessible cabins
4. never seen a specific deal on accessible cabins.
5. On the lines I’ve sailed with Balcony, Mini Suite, Jnr Suite and Suites have balconies