if I had your tank I would put 15-20 in there. I have a 29 that is very well planted with 10 tiger barbs 12 guppies 5 albino corys and a baby albino BN pleco. and a #$%%##%$ of ramshorn snails. Will most likely move the guppies eventually but they are the ones that established this tank and so far everyone is coexisting amazingly well. Sunsun302 dual filter sponge, organic soil capped with pool filter sand. Good luck!! anxious to see how it turns out once u stock it!
Edit: one piece of advice if I may.. I would put your heater more horizontal behind your rock pile to hide it more and for when you do WC's it doesn't go below the minimum water line unless you unplug it before maint. I personally don't
I always unplug the heater one time I didn’t and the bottom of the heater shattered and spit black sand stuff all over the tank. And I will be putting 18 tigers in it I’ve had them for a while in my 55 but I want to switch up the 55 and I think the 40 will be good for them.
And here is a new pic of the 40 the other one was old and idk why it looks green
no they won't mess with you plants... maybe the occasional nipping but for the most part will leave them alone. but fun fact tiger barbs will eat watermelon....
as for how many ive been told 15-20 in my 38 gallon tank.
my current stock is 16 tiger barbs, 3 cory's, and a pleco.
Just to throw my own (meager) bit of info in here,
I have my main 60-gallon goldfish aquarium, and a few months back bought a *bunch* of (different types) of Anubias and even a package of Cardinalis. They're all growing but all have problems, algae growth and some deterioration, they're growing but it's not great, will take some work, etc.
About 4+ months ago I had to set up a hospital tank, and it wound up being a (small enough) aquarium for my kitchen, and has some (small) Tiger Barbs in it. I also bought maybe 4? different Anubias plants (I accidentally threw away all my packages and the 'master list' I wrote up, so I have no idea which species are which in any of my tanks now, awesome) -- and a Rosette sword I believe. So obviously the TANKS are different, different sizes, different fish, different filters, but my *care* for them is pretty much the same (I'd like to think..) and the plants in my Tiger Barb aquarium are *thriving*. All the Anubias plants look *great* and the Rosette Sword plant, while the original leaves have yellowed, it's replacing them with beautiful green new leaves.
Contrast this with my Goldfish aquarium, where it's a freaking battle and a half *just to keep the plants planted to the gravel* since they are among savage fishes who just try to eat everything all the time every moment of every day.
So in conclusion, to me, Tiger Barbs are perfect for planted tanks, and yours looks *outstanding*, I'm very jealous.