I have 20 observations, time series data, lag order selection criteria (FPE AIC HQIC SBIC statistics). These show that I can choose 4 lags, co-integrated equations based on max trace statistics, showing that there are 4 cointegrated equations in the system. Taking into account that the sample size is small, what should be the number of lags and cointegrated equations(rank) for running VECM?