Well i'm not sure what boundary you have in mind for too advanced, but i'll tell you what i've learned about brawl's marth and marth in general that carrys over from melee.
(personal tactics)Don't overuse roll, i prefer spot dodging or dropping shield for the initial dash (tapping joystick quick in 1 direction, you can double, or triple tap to confuse opponents and move more unpredictably, if you quickly tap in the other direction after about 1/8 of a second after the first direction you can do quick fakeout turnaround from dashdance). The beginning of the dash is you best means of ground movement IMO.
(Platforms) On a stage with platforms try to go underneath and Utilt, Up-Smash or U-Air players above you, Fairs work here too if aimed well. Take advantage of your rediculous range of aerials, Short hop fairs and move left /right to space yourself with your opponent, or double fair a shorthop ocasionaly. A SHFair at peak of jump fast falled into d-tilit spam is effective both offensively and defensively.
(Edgegaurding) As for edgegaurding, chase oponents off stage with fairs or Bairs, certain characters recovery's such as Ike's side-B, or Wario's Up-B don't auto sweetspot, so use a d-tilt, or forward smash on them if you see it coming.
(Grabs) Grabs are still good, but much less range. If you grab someone near the edge of a stage facing off it, forward throw into Fairs, or if they DI wrong a fair -> dair spike. if you grab while facing away from edge, down-throw, now in this instance either immediately forward smash, or if you see a jump coming, shorthop and bair, and chase off with fairs. A Pseudo chainthrow marth has is to intentionally grab the opponent, allow them to break free and immediately dash grab them and repeat until they get out of it. (Once they expect it it wont work anymore.) If you can learn turn around grabs you will find good use for them. They are dashing in 1 direction and hit the c-stick in the opposite direction immediately pressing grab, to grab behind you.
(Approaching) As i said earlier fairs are always good approaches, or if you approach from the ground alternate between dash attacks, dashed B-Forward bladedance combos, a dash -> sliding upsmash and dash->shield->Up B. To explain in more detail, Marths Dancing blade is very good, it will work even in the middle of a dash, and will stop your movement immediately, and can be used either behind or in front of you (VERY GOOD). Upsmash can be done at anytime our of dash, just hit Up on your C-Stick. On Up-B> out of shield dash, dash forwards at someone, when you see the initial dash end and marths legs start to run you can shield cancel it, this is done by pressing shield at at this time. Then when an opponent is near, Up-B out of shield. Mix up your ground approaches so they don't get predictable.
(edit) another good approach i forgot to mention is to dash - > SHNair, and pull back on the joystick, it works well for luring opponents into the second hit of the Nair, as they expect you to get closer with a fair.
(Tipper & Basics) Something very basic i forgot to mention, all your blade attacks have a sweet spot called the tipper at the edge of them, this will do extra damage and increase knockback, learn to use it efficiently. Marth's main priority is infront or above him, so try to keep enemies here. (Uair is very good for damaging and killing, good timing will make it very hard for your friends to stop.) Learn to reverse Fair opponents, this is jumping backwards and doing an aerial forwards, which is very hard to get past if used well for opponents with small hitboxes on their attacks.
I've said alot, but some of my best advise to you is to make some good friends on WIFI and learn from them, as well as to read any posts made by M2K, he has good situational advise it's useful if you can find the opportunity for it. Good luck have fun, PM me if you want any specific help on something.