A few things:
-This was one of the slowest battles I've ever seen. Roll. Wait. F-tilt. Roll. Roll. Grab? Roll. D-tilt. Sex-kick. Roll. You probably won't place well in anything playing against a Yoshi whose only moves are smashes, fairs and rolling. I'm no pro either, but get out to some real tournaments, it really helps.
-Wavedash somewhere. Please. Move faster.
-Use more missiles. Use missile cancelling and chase your own weapons with wavedashes, then tilt/smash/grab/sex kick where appropriate.
Anyway, you mentioned Marth and Falco...
For Falco, use plenty of fairs and uairs. They hurt fast-fallers plenty. Spam upB if you have to against them, especially if they try to shine combo. Screw attack screws space fuzzies.
With Marth, and effective edge-guard can be walking off stage and sex-kicking if they approach low. If they don't, fire high missiles to dictate where they recover. Also, try to use wavelanding to keep away from his sword range. If Marth catches you in a fair juggle, DI as best you can. He can take out missiles with his sword really easily, but keep it up anyway. Sometimes all it takes is one missile to leave him open to some damage.
Also, on a final note, I think you might be looking more at Samus than your enemy. Keep your eyes on the opponent in battle, it makes reacting much easier. Good luck!