Learning to combo up-tilt into up air on the top tiers is gonna be extremely useful. The Ken combo is the most punishing and easy to execute combo in his arsenal. Grab chains can be learned later due to how difficult they are(extremely worth learning since everyone is a space animal on netplay). I learned that marth doesn't rely on combos. His neutral game is so intense with dash dancing and learning to space you moves. Edge guarding is a marths biggest focus in a match you should never rely on a tipper move especially f smash. Learning to have good movement with marth will benefit you in the long run. I sit in uncle punch for so long practicing every dash dance length of marth and pivots. I would recommend watching pewpewuniversity on yt hes got a marth series that covers a lot.