Quick analysis: your survival DI is REALLY good. Your combo DI is REALLY bad. Lol you gotta DI out when you get grabbed and when you're getting fair'd all over the place. Also, when you're getting edge guarded by marth, you have to react well. If they jump, you should DI up and away for the fair, then DI up and in; the reason for this is that when you DI up and away on fair, they can only hit you with another fair (and then they have no jumps left, so DI up and in is ok). If they decide to nair instead, you can react to that pretty well. Sometimes up and away DI will get you out of the second hit as well. You DI'd fsmashes well.
You tried to challenge marth's fair with your own a bit too much. When you're facing marth, his fair will always beat yours. Sometimes you can beat out his nair, but don't try to just fair your way through his aerials. Bair is a much more solid choice - it will at the very most trade with marth fair.
Your recovery game was all over the place. I really liked a lot of those air dodges to avoid the gimp setups and everything, but sometimes your normal recovery game was risky. On yoshi's story, using the down-b recover is never actually safe vs marth. Your opponent didn't punish you for it, but just be careful with it because a marth more familiar with the matchup will punish those.
One more thing: don't shield grab marth's nair. I know it looks tempting, but any self-respecting marth player will cross you up and dash dance. I like to stomp / bair in this scenario. I know there was an instance in the last game on BF where a stomp would've connected. I remember doing this to cactuar a lot and it hit every time until he adapted and started up tilting. If you're in your shield, up tilt is punishable with reverse up-b OOS.
Overall good set, you seem like you have solid fundamentals and knowledge in the matchup. Keep it up!