Posted: 21/05/2014 at 19:40
It depends on what variety of tomato plant is being grown: determinate (bush) no picking out, or indeterminate (cordon) - remove side shoots. The root stock doesn't change the variety - just makes for a stronger plant and will need at least a 12" (30cms) dia pot as the roots are very vigorous and will need the space to grow well.
If for instance, you are growing 'Red Alert' then it is a determinate and you do not pinch out the side shoots: If the plant is say 'Shirley' or 'Alicante' or 'Ailsa Craig' then they are all indeterminate and are best grown as cordon.
Best way is to google the variety name and see what the type is but whatever it is don't start using tomato feed until the first truss has set fruit or you will get loads of foliage and little fruit.