Most exchanges have a minimum, but gekko itself can handle very small amounts.

Also, keep in mind that for a lot of exchanges, a microtrade smaller than 0.000002 bitcoin (200 satoshi) or less would be a bad thing since the fees are usually rounded up to the nearest satoshi (8 decimal places) and the lowest fee possible is 1 satoshi (0.00000001 BTC)

Either way, it'll work with 0.00000235 bitcoin just as easily as 5000 bitcoin, though I'd recommend start with less than 5k BTC
(that was meant as a joke, testing with over a million USD is a bit crazy).