I believe that the second rating field with the stars is not currently possible. It has been requested. You'll find that the Media Center team is VERY responsive to user suggestions but I think this might be one of those suggestions that is more complicated than it seems.
Second suggestion has been requested, by me as well as others, for the same purpose you suggest. I suspect that it may be the same problem as above.
The work around is effective but not pretty. There is nothing special about the values in the rating field so you can use your new rating field and give it a 1-5 rating by typing it in. After rating some songs, the drop down should populate with the values you have used. Obviously this does not have the same ease of use that you are asking for, but the field can be used in smartlists/view schemes as if it were the original rating field. Same with the checkbox, you could just use y/n.
I'm not speaking for J River, just what I've picked up from the boards.
Enjoy MC!