A little late to the party but glad you decided to go with David Klass. "$2150+ tax + $500 estimate for expanding halo (this was without knowing any dimensions) + $250 mounting fee" sounded like they had to make extensive alterations to the ring and that just spells trouble.
Halos help make the center stone look bigger or provide more finger coverage. As such you'd want one that integrates well with the center stone. If you want the center stone to stand out then I'm not sure why you'd even want a halo. The higher setting does post a risk or damage or loss of the center stone so most caution against it. If that's the style you two prefer and find the trade off worth the risk then you should go with it. The ring is for your enjoyment and not to please others.
For an antique cut do you have any color limitations? RG and antique/OE cuts compliment each other nicely so you can go pretty low in color.
Halos help make the center stone look bigger or provide more finger coverage. As such you'd want one that integrates well with the center stone. If you want the center stone to stand out then I'm not sure why you'd even want a halo. The higher setting does post a risk or damage or loss of the center stone so most caution against it. If that's the style you two prefer and find the trade off worth the risk then you should go with it. The ring is for your enjoyment and not to please others.
For an antique cut do you have any color limitations? RG and antique/OE cuts compliment each other nicely so you can go pretty low in color.