The illustrious 18 captures most of the benefit of deviations. And deviations themselves are a pretty small benefit compared to spreading bets properly. So, knowing 35 deviations is definitely not necessary.
If you’re going to learn deviations, make sure you know the ones that give the most value first (insurance, 16v10, 15v10, …). Although, you might not use the ones for splitting 10s for cover reasons.
After that, you might be getting bored, so adding more deviations is a good way to keep it interesting. More is always better as long as it isn’t preventing you from playing everything else correctly.
There are pros who know and use hundreds of deviations.