I am quite new to the theory of RNNs so please excuse me if the question is trivial. I am trying to fit a multivariate LSTM neural network to predict stock prices from a firm in the S&P 500 list. I have seen many applications where the opening price is forecasted using the stock's own closing price, trading volume, highest and lowest trading prices.
However, I was wondering whether it would be sensible to try and forecast the firm's opening price using other firms' opening prices (specifically, I was thinking of other firms in the same sector in the S&P list, e.g. healthcare or IT sectors depending on the chosen firm). Since prices in the same sector are likely to be highly correlated I thought this could be a good approach. However, this would create a dataset with many features (much more than in the examples I have seen so far) and I am thus worried that it would lead to overfitting. Could this be mitigated by increasing the size of the time series?