Taking a stab in the dark here but let me know if I am close. You are using GARCH and ARIMA on the options pricing data to identify moves in the market. Once you identify a move you try out a bunch of different combinations of buying/selling puts/calls. You then take a look at the possible positions and see which wouldn't require an absurd collateral and execute on it?

For something like PLNT how did you run a backtest? It seems like there is only ~1 month worth of data.