What Gcse subjects do I need to become a vet and what are grades should I aim for?Watch
For GCSEs i would recommend choosing Triple Science. From my knowledge there is no other optional GCSE that you need. Taking a foreign language could benefit you so that is something to bare in mind but is not a requirement by any means.
Maybe look into STEM subjects for your other GCSE choices. For example, computer science or further maths would be a good addition.
It does not really matter what you choose for GCSE, even to become a vet, these are only suggestions. Focus on Science and maths and try and get good grades in the rest of your GCSEs and you should be fine.
As for practise papers there are loads online. You do not need to start though until year 10 but if you would like to look through some to help choose your options or to get a better idea of what it is going to be like then that is a great idea. For now i recommend just working hard in your classes and completing your homework and enjoy year 8 and 9.
Hope this helps
Edit: Sorry i forgot you also asked about requirements. Obviously your A levels are more important but i just had a look around.
You will need grade A-C (9-5) for at least 5 of your GCSE subjects wherever you go according to UCAS.
Nottingham for example offers a good course that is 5 GCSEs at grade 7 (including biology and chemistry and either physics or maths) and a grade 6 in English language and Maths. (one of the top unis according to google for veterinary medicine).
A levels they offer AAB.
Personally i would go and have a little look around at Unis and see what they offer and see where you want to be aiming for. See what is the lowest you want to aim for kind of thing.