i haven't played GTA IV in a while, but from what i remember that's still pretty early in the game. there are some pretty challenging missions later on, so just hang in there. it's a good game and i personally preferred it to GTA V.
I liked GTA 4 specifically because the mood of the story and overall pacing of the game was a little different from the other GTA titles. Rest assured there are some difficult/frustrating missions that require you to play really well, but nothing impossible.