It is impossible to practice too many question – the more practice the better.
Hopefully you are using a Revision Kit from one of the ACCA Approved Publishers in which case you should aim to practice every question in the book.
If you are somehow downloading questions from the internet then apart from the fact that it is illegal, there is a risk that not everything is examinable in the same way because of syllabus changes and exam format changes. Questions in the Revision Kits are all updated for this.