This will be a really great event.

One option with the nominations could be to allow everybody to nominate then trim back the field based on evening the numbers, for example:

10 ROW Runners and 12 from the UK would mean that the UK captain would have to scratch two from the field.
That would mean equal representation and way less admin for the two captains.

On the track and going Ascot seems reasonable for the first time around although next years captain of the winning team this year should then be able to nominate a track kinda like Davis Cup tennis.

On the going I have to agree with Dave F, breeding changes over time for example my current stable are really Good-Firm runners although most recent breeding a few weeks back showed that the better horses coming through were Good-Soft so I have noticed a definate shift of preference in my own breeding, Good being in the centre of the spectrum gives the majority of horses a chance to compete where the other options cant do that.
Every event like this should really be on good.