How many turbo snails?

How many turbo snails can I put in a 180 gallon FOWLR stocked with large fish without worrying about them starving? Right now I've got 2 semi large ones who are eating diatoms, but I don't want to add more because I'm not sure what can be supported once all the diatoms get eaten.

Final stocking will probably be

1 porcupine puffer

1 large dogface (haven't decided on regular dogface or Guinea fowl)

1 bird wrasse

1 harlequin tusk

2 blue jaw triggerfish

1 Niger triggerfish (maybe)

1 Naso tang

1 smaller marine angel (in lieu of second trigger)

So probably 7 or 8 large fish.

Is 2 good or should I get more?

Current stock is 1 blue jaw and a bird wrasse with a porcupine puffer in the next week or two.