My question is;
How much effort and practice is required to give yourself a chance of a degree place at a respected college/school.
Is it possible to adequately study all your other subjects and have a social life, or do you a young age have to "go for broke" to aquire the necessary enrty level techincal skills
Sorry to sound harsh here, but I've discovered this the hard way. If a child is not a very high Grade 8 standard on piano/violin by the time they're about 14, it's really, really unlikely that they'll go on to be a pro classical performer. And frankly, to attempt that path is going to make any child very unhappy. You've got to remember there are some very, very talented kids out there who just find it easy.
Even most graduates of the top colleges -say, the Guildhall or Royal Academy will end up spending most their time teaching with maybe a few concerts. That's just classical performing though. If you're talking composing, recording, media stuff, whatever else, as discussed above I think it's a combo of talent and perseverence.