I think the only challenge for investments with small capital is that we have to wait for a long time.If we invest a small amount and we want to earn huge amount of profits then we will have to let our money grow for a long time and have to sell at a very high price and this require a lot of patience and a huge trust in the coin in which we are investing.
The only challenge for investment with small amount is your patience in waiting because you put only small amout then you want to get big profit. But for me its better to put small amount in an investment because the risk is lower than put higher amount then the risk is higher, atleast if there's something happen you only have smaller amount to lose. Just think the good side of investing with small amount atleast in the end you will get profit.