First Match vs Marth:
Try working on your combo's at 0%. Dthrow -> utilt -> uair -> fair -> grab, dthrow -> utilt -> uair is a really nice combo. You might try easier variants first: dthrow -> utilt ->uair -> nair, or fthrow -> running usmash. At higher percents, uair -> nair is a good finisher. You did a nice utilt -> thunder on marth on the first stock.
Also, work on punishing marth when he fails to sweetspot the ledge. I believe it happened 3 or 4 times during that match. You also need to speed hug the edge against marth more often as he's trying to recover. Speed hugging/edgehogging usually gives you a free stock or a free aerial. Nice edgehog on the second stock btw.
Be careful with skull bash. It can be rewarding at times, but often, its very dangerous. You lost your second stock while SB'ing. The easiest way to hit with SB (especially on the tilting stage of Lylat Cruise) is to charge it up and act like you are going for the edge, but instead, go right above the edge. This usually only works once though. Never use SB when you are close to your opponent.
From 4:00-4:15, you went from 68- 110% while you were trying to return to the ledge. If marth spaces himself like he did, do a ledgehop tjolt. If he gets closer, do a ledgehop aerial, but if he stays there, keep doing ledgehopped tjolts. If you really need to return to the stage, ledgehop -> QAC works nicely.
I admire your perserverance. You got marth from 0- 150%+ even though he had a 100% lead on the last stock. You guys were neck and neck (both at 150%+) at the end, so props for not giving up.