I'd say maybe 1 or 2 on from Reading, about 3 joining in Oxford, 1 or 2 more in Banbury and perhaps 3 or 4 joining in Leamington Spa. At the most. It should be very lightly loaded indeed (by CrossCountry standards!) because (a) it starts in Reading and so won't have any through traffic from the south coast, and (b) it goes direct from Leamington to Birmingham via the GWR/Chiltern Line and avoids Coventry & Birmingham International, which would otherwise generate a lot of traffic.