To simulate the whole train () process (including CV, etc.) with various subsets of the training set (10%, 20% ... 100%). In principle, I would like to evaluate whether your training set size will reduce the large variance. For 2. you need the error rate when changing the mtry hyperparameter, but if I understand what you mean, trainFit will calculate the error rate for different CV-folds (although, I suppose, the last figure is the average for everyone).
do my homework