If someone says they're new, are new to the term float cancelign which every peach player here happens to know of and are new to these forums, I do not think it's a mistake on my part to consider him newbie. >_>;;; Not to mention he's here asking for advice against sheik, so... And I also just poked at you for fun, cause the way you typed it how badly he pwns you. No need to take it seriously.
Also, cc has nothing to do with smash DI. Crouch canceling is where you reduce the knockback of some attack that can be cc'ed, if it's not a meteor or doesn't have too much knockback or hitstun. Smash DI when you use the stick and some cases c-stick to affect your trajectory during the hitstun of the move you got hit, which makes you move around during the hitstun and greatly affects your trajectory.
With sheik's traction it doesn't have anything to do with sheik's ability to cc stuff, only if it were someone like luigi or ic then the traction would affect their crouch cancel countering abilities more and they'd need to use cc into dash into stuff more cause they get pushed back more. Also peach can cc a lot of stuff to 70-80% or so and she's lightweight, sheik is heavier so I don't know where you're going with that. >_> Sheik's arms and legs are long, sheik has a very quick dash and good grab range, so sheik is able to cc good amount of stuff to 70-80% or so, depending of the actual attack. Also it's very good to mix up and not always dodge, even when sheik's dodges and overall evasion skill is very good. Baiting someone to attack with something crouchcancelable and then punishing with a combo that takes a stock is imo, quite effective, moreso than not getting hit and opponent getting away without your punishment and still is in position to predict what you're gonna do next or where you're gonna evade. Samus relies on cc to more extent than many other characters do, but that's where her strenght lies. Sheik has many strenghts and in overall is a flexible characer, so it would be a shame to not use sheik's cc since it's good. I do think learnign how to cc things may be more vital to some characters than others, but it is a reliable way to punish something with every character and thus vial for every player to learn.
Edit: Peach's highest part of her upsmash is not the sweetspot part, it's on her shoulders, the middle hitbox, which is also very strong.