The contribution is $ 1,000 in Fiat or you can invest in Bitcoin, for example, but in the amount of $ 1000? It is simply not indicated.
It cannot simply to say if bitcoin would like have a minimum amount, but seems it just the same as the fiat. Since the bitcoin is volatile, i think there is no minimum.
I also think that there is no limit to this. How much do you want to buy so much and buy. If in doubt, write in support