I use Fluval Stratum or Seachem's Flourite substrate but I also do live plants which is what those substrates are for; and shrimp. With those, I don't recommend an under gravel filter. If you're going with regular gravel, the under gravel filter will be fine. As for later thickness, I would keep it the same as you normally would
In my invertebrate (shrimp, snails, etc) I use sponge filters.
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