While not exactly what you are looking for, you could remove the "single value" constraint on the attribute and then move the attribute in the "Create" layout for the object type to move it into the main group. If you put it above the "Description" field, you could use the description box as a place to further specify the "Other" value. I have an example here using "Drop Down" style.
The problem with the radio buttons method of showing the values (can be done by editing the attribute as it is applied to the object type in the type and attribute manager and changing the "Selection List Style" to "Radio Buttons") is that by definition, you can only select one radio button value for the attribute. So, you would need multiple values for the attribute, where each instance of value would show ALL the radio buttons, and only one can be selected - which is very confusing in my opinion.
2) Perhaps there is a more elegant way to bring in the "other" field, but in the meantime what I did was simply add another attribute named XXX Other and made that one a field instead of a radio button. For most of them I also made the main selection (with the radio button) a required field with nothing preselected in order to force the creator to address it.
3) You can rearrange them in the layout section when defining your subtype. I created several groups and sorted the attributes based on their position in the product. Within each of the groups I was able to just drag and drop the attributes into different positions. There is a button that allows alphabetical but that really screws with the sequence in my case.
