Okay, I hope this isn't a re-post, I've looked around and couldn't find this information specifically.

How many gallons per Betta in a tank? See, in the new tank I'm getting, you can fit two tanks on one stand so I was going to have a goldie tank and a Betta tank (because they're stunning!!) The tank will be 40 gallon on average and I've read elsewhere that it's 1 gallon per Betta (not that I'll be having 40 Bettas, though that'd be nice! Hehe)

Any help would be much appreciated ta.

You can only have ONE male betta per tank, or you gonna have to divide the tank into sections to accommodate more males. If you don't want to divide it, then a 40 gallon is a very nice tank for a community female betta tank.

My suggestions: why don't you buy a bigger tank for the goldies, and leave a small section of the stand for a small 5-10 gallons male betta tank?

Ur call mate.

So 40 gallon would be FAR too big for Bettas? Wow I'd have thought that much would've been good for them!

How do i establish male from female bettas? Are they like birds in the sense that males are prettier? Obviously I have alot more research to do - I won't be getting the bettas YET, but I'll get the tank and stuff.

Well, 40 gallon for male bettas are overkill, IMO. U have to make LOTS of divided sections to fully utilise that big of a tank. Do you know that males will almost definitely kill each other if they're put together?
40 gallon is absolutely fine for female community tank, however, and I'd say u can have up to 20 of them quite comfortably. But females are often feisty creatures, and expect lots of fin-nipping & chasing, especially for the first few days when they establish that hierarchy.

Male bettas tend to have longer fins than females. In short-finned varieties, males will usually have longer ventrals and females will have an ovipositor (a white dot under the body).