As previously discussed, the big things that hamper Luigi are his reach and his poor traction, as attacks that hit his shield will usually push him too far away to punish you unless you used a particularly laggy move or whiffed. This makes it safer to pressure Luigi with aggressive aerial approaches rather than the usual defensive play we employ against grab-happy matchups, as his only defenses against our Fair, Nair, and Bair are his fireballs and his own aerials - the former of which are slow enough to react to and the latter of which are very quick but much shorter ranged than Ike's swings. So pressure him, but continue being mindful of your space and momentum so you don't jump straight into an Fair. When pushed away, he may respond with dash attacks, which while extremely punishable on shield lasts an annoyingly long time and I believe has priority over our jab, so don't think the shield push is a free ticket to chase him.
Also previously mentioned, be prepared to shield when under him. His air speed makes his Nair somewhat punishable on shield, and Cyclone is punishable as well, but the danger is just how quickly and suddenly he can toss them out.