Luigi's ground moves for the most part are great launchers that set up into his aerials, so being strong on the ground and in the air are essential. Spend the time to learn the %'s and know when you can do Dmash to Dair, or when you need to throw in an extra Utilt to send them higher for example. Luigi's 2x aerials are a big part of his game, along with single aerial/waveland. 2x aerials MUST be L-cancelled and single aerials should almost always be wavelanded. Cover your 2x aerials with jabs/tilts, your opponent will 9/10 times try to attack after you 2x aerial, so you can catch them with a tilt or jabs, and then go from there.
2x aerials aren't that unsafe as long as you L-cancel and cover them with jabs, tilts or shield dashing. Approaching with an aerial mentality might work a little better because u have more options (single aerial/waveland, 2x aerial/cover moves, single aerial/waveland/grab, etc.) It comes down to reading your opponent and seeing which game works best against them, try not to go into a match with a strict plan already, all players are different.
Up B is not a strong plan at all, unless you're edge guarding sheik. Yes, it's strong and flashy, but there are too many downsides to that move for it to be a recommended strat. If you miss it against a good opponent, you are sure to take a good 20 - 30% in damage, not to mention being knocked off to be edge guarded, or just die altogether. Dealing 1% and taking 20 - 30x that much percent is not a good trade. If the Up B is blocked Luigi goes flying away fromt he opponent, and can be hit right after. Another common situation is if you see an opportunity to use it, and you miss by accident. Not only do you deal only 1%, but you reset your opponent while you're in the air, and you're in trouble. Doing an aerial/smash is MUCH safer and efficent.