Against diddy, it may not be a good idea to sh your pikmin toss, since diddy will throw the banana when you're landing. In fact, may not be a good idea to pikmin toss that much at all, since they usually arc above the bananas anyway and rarely block them.
Excellence, stuff like "which way should I roll?" can't be answered. You pose too many questions that you need to find for yourself through playing them. Every player is different, it's up to you to observe their patterns.
Anyway, grabbing isn't a good idea in this matchup imo. Stuff like dash attack can hardly be punished by a grab since a second attack or a retreat can be started right after it, and our lack of shield armor makes it difficult to find a space where we can safely grab. I really don't like this matchup, but I play it all the time

In the air, his fair> our fair, and it is fast enough that they can fairly easily bait an airdodge/ whistle, and attack after. God I hate this matchup...