That specific error message is because there's a minimum amount for trade, but you didn't have enough funds or assets available in your portfolio on the exchange. You can look in exchanges.js for the minimum values on whatever exchange(s) you're planning on trading on.

I don't have any advice on how to configure DEMA...

I recommend switching to MACD.

The standard values which a lot of people have good luck with is:

Short @ 12
Long @ 26
Signal @ 9

If you want to see what those values do, a good way to visualize and look at historical data is by looking at old charts on a site like bitcoin wisdom.

https://bitcoinwisdom.com/markets/bitfinex/btcusd << the default MACD settings are 12 26 9 so just turn on the MACD indicator and have a look (it'll show up at the bottom once you enable it)

Note: bitfinex currently looks like it might be the exchange with the most volume at this time...

askmike just accepted a pull request for bitfinex support too, so you can even use it with gekko

I hope this info helps.