How to set size of hidden state vector in LSTM, keras?
If by vector size you mean the number of nodes in a layer, then yes you are doing it right. The output dimensionality of your layer 
is the same as the number of nodes. The same thing applies to convolutional layers, number of filters and output dimensionality along the last axis, aka number of color channels is the same.
I am currently setting the vector size by using model.add(LSTM(50)) i.e setting the value in units attribute but I highly doubt its correctness(In keras documentation, units is explained as dimensionality of the output space). Anyone who can help me here?