Water depth doesn't really matter. I've bred in 3 - 50cm water with fairly the same result. Just remember that the deeper the water, the more energy your male will use to care for his eggs/fry.
Eggs caught between gravel that decay will foul up your water. Their waste will also get caught between the gravel. Since you can't use filters, IMO this will affect your fry in the long run because once they've hatched, siphoning will be difficult (without sucking out fry).
...I'm worried about the rocky bottom, the eggs might get stuck between stones and the male unable to pick them up and put them in the nest? I've always used bare bottom tanks,and i've seen sand used without issue because it's flat.
There has been one way. Regular filter head, find an aquarium sponge cut into the middle about halfway and slide onto your filter head. Best used with an adjustable flow filter if you can. :) I'm doing that next time to ensure there won't be mini cycles, and easier to clean.
Just want to check (because you haven't mentioned it, not because I don't think you'd do it) that you have places for all the male fry when they start to become aggressive, food for all the fry and potential homes for them all too (in terms of shops/private buyers etc that you will sell them to).
I also want to add a word on breeding VTs - sadly (and silly-ly, I think) they are not considered high quality because they are a 'boring' tail type, and they will be harder to find good homes for than 'higher quality' tail-types like HMs. Not trying to put you off, and I would certainly buy a veiltail, but just a warning. :)
I agree because here VT is sooo common but, if you have sought after colors coming out (depends on every area, and how big the area is!) you could re-home quite a few. Even asking some LFS to house some...
Sniper's a veil. and i willingly spent $16 total on him, because he's just so unusual and beautiful.
i think.... normal colored veils are what you should stay away from. reds, blues, mixes of those two... you see those everywhere, and they're the ones that stay at the stores forever. unusual colors are what you go for with veils. Sniper's a white and blue marble, and not just blue. deep blue-green. that's why i wanted him so badly. the unusual ones go quick.
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but, if you have sought after colors coming out (depends on every area, and how big the area is!) you could re-home quite a few. Even asking some LFS to house some...
