To expand on Etiennes' reply:
One of the schools I used to deal with always held appeals in the school, until 2 years ago when the new clerk insisted on a neutral venue. I did do an appeal recently in a school, but it was very short notice (less than 1 week) the day before the end of term, and the clerk did not have time to find a neutral venue. Both sets of parents were asked if this would be acceptable to them at the time of booking the appeal, and they agreed (otherwise they may well have had to wait until after the new term started). They were held after the school day had finished an the staff had gone home. But this was exceptional.
2)Also, how do I know the three panel members don't have any connections to the school. Do I ask the appeal clerk whether or not they do or do I just assume they don't?
They may introduce themselves saying that they have no connection. You could always google them along with the school name, but I would assume 99% that they're neutral.
As for oversubscription, they key questions to ask the school side are "how many pupils have been admitted each year", "How has the school coped with this", "Has having such a large number over PAN affected the results" (check stats for KS3 SAT scores & GCSE / A results - hopefully they will have been improving, so they can't argue that the large number of pupils affects negatively), and finally, "How many pupils are currently on role for Year 8". Don't be grumpy with the school side - ask nicely. If you forget, there's a chance the panel may well ask the same questions.
Assuming that the school is improving in results, there are less pupils on role than they started with and it does not make it the largest year group in the school, you can argue easily that taking one more will not prejudice the other pupils.