I could definetly tell when you were going in for a grab, and that peach punished you with a spot dodge -> down smash. In the millisecond before going in for the grab, if you substitute for the side b combo you will hit peach. The first slash of the combo goes into the spot dodge, and the second one hits them up, and if they DI incorrectly then you can hit them with the third slash, which has the knockback of a tippered ftilt.
Also, you don't have to fsmash everything for a kill.
Hmm... I actually liked your use of the fsmash -- personally i've been working on incorporating it more into my combos. Getting the fsmash -> edgeguard is way better than tacking on an extra 20% damage and blowing your opportunity to edgeguard. Even when you used it outside of a combo, you were pretty good about only using it when peach's movement (and thus defensive and countering options) was limited. Azen style, man.
Sytos is right about your approach -- it got to be a bit obvious when you were gonna go in for a grab, and the peach started to spot dodge and punish (should've done it even more than she did). But as an additional suggestion, I also recommend waiting until the peach picks up on this, and then starting to go in like you're gonna grab but instead run right past her through her spot dodge, then dashcancel and tipper her backside as she comes back up. Works nice for me against better players than myself.
As for your recovery, the peach really let you have the ledge for the most part, so I didn't see any point in varying it up unless she does.
You tended to fthrow a little too much -- it would have cost you more followup opportunities if the peach DIed better. Even so, mixing it up would've set you up more often.
You also daired (often out of sheild) too much for it to be really effective. When you missed it, you got punished as you were falling back down, and when you landed it, you weren't generally able to follow up. Mix that up more.
Finally, I know that fair to dair combos aren't so great in PAL, but the couple I did see you go for, you seemed afraid of moving too far off the stage when you in fact had plenty of room left for recovery. If you are going to do it occasionally, practice it until you feel comfortable finishing the combo.
Nice marth in general. Definitely very good for your first real tourny.