approach i used is same as yours.
but answer is different.
Minimal DFA i obtained is accepting a(a+b)*. and there are 3 stated in minimal DFA. one initial state. one final state and one dead state.
in the table where you converted epsilon NFA to NFA, row 2nd and 3rd is incomplete, as state 2 and 3 both will go to all the states 1,2,3 on input a and input b. please check it once.