My stage preferences
FoD > DL >> BF > PS/Yoshis/FD (The last three I couldn't really decide on, I don't hate any stages in this MU)
You can punish dtilt with a walk up ftilt of your own iirc, but it's a tight timing.
You have to make crazy use of crouch cancelling at low percentages, that's how you get Marth into the air and it's also how you take early stocks. If you get an early stock than you can play war of attrition and the match is yours.
Have a great mixup game when you're recovering, save your double jump by mashing out of tumble and doing an airdodge > grapple. Mix things up with fast/slow fall and bombs when you're coming down from a juggle. I guarantee you're going to feel pressured to fast fall down with a nair or dair, but eventually that will become an easy bait.
If your DI is good enough, you'll either die early from a low percent combo, or you'll live to like 200%. Marth upthrow kills you on FD at around then. For some reason it's a common occurrence for me to get hancocked on FD so I have that little piece of info to share.
You can't miss edgeguards against Marth, in fact, you can't miss edgeguards ever. But missing an edgeguard versus Marth can be the difference between a 65% kill, and a 135% kill. And between those two percentages, you will have taken serious damage or even lost stocks. The big thing that Marth players use to get the ledge back is save their jump and stall with side-b a lot. Keep a careful eye to see which recovery options he has left, and when he will be within sweetspot range. Marth players absolutely hate having to up-b onto stage, remember that because it can be the hesitation that ends their stock. If a Marth player steals the ledge from you by baiting a roll onto stage or hitting you with the UpB, recognize that you got roasted and make adjustments by rolling at a later or earlier time. And if they don't mind landing on the stage, use invincible nairs, it's an incredible tool in every matchup, but you have be good at timing your ledge invincibility to take full advantage of it.
This MU is definitely Samus favored when it comes to how they edgeguard one-another. But I feel Marth has the advantage on-stage. Just take advantage of having a better position vs him, and punish him when he's above you. Also, feel free to use a bunch of missiles in this MU. Marth doesn't deal with them as well as many other characters. Marth is also combo fodder so you can get some sweet and spicy 55% combos from a hit at 0%.