Picking training data
In order to validation you can choose different methods such as k-fold cross validation, repeated splits and Bootstrapping. It seems what you aim to do is 2 fold cross validation and yes it should be random. You should be careful, and it seems your training data and testing data are very different.In this case, you;ll not have a model with a good performance.Try to find a way and make your training data look more like the data on which you want to implement your model. In this case you might want try 10 fold cross validation (for instance)