Weegee's fireballs are terribad, possibly one of the worst (if not the worst) in the game. They have pitiful range, slow, and meh priority (basically inferior to Mario's fireballs in almost every way). I believe you can cancel his fireballs with Din's, albeit Din's also being slow. Yeah I wouldn't rely on Nayru's Love too much unless you get a hard read (for example, if the Luigi likes to roll close behind you a lot and isn't used to shielding NL long enough), and I wouldn't bother using it to reflect fireballs much either. If Luigi puts you in a terrible position to recover, you have the option to Love Jump, but remember not to overdo it, as the move has cooldown, and he can bait your landing and punish.
His aerials are annoying, particularly nair, which has great priority and killing potential. Tbh I would not rely on Zelda's upsmash too much to counter his aerials, unless you have good spacing (though f-smash is a better spacer than upsmash).
His f-smash and upsmash are very powerful. His f-smash can also be angled (angling it up can kill you ridiculously early, even with good DI). His upsmash usually won't kill you as early but some Luigis like to charge it a little bit, and it's not bad for punishing landings or if you're air dodge happy like I am, this can be troublesome. His upsmash also has some horizontal hitbox due to how big his head gets, and he's also a 'slippery' character, allowing him to do some sliding upsmashes that can catch you by surprise.
His recovery is... well, not the best thing, but not the worst. He can gain a horizontal boost with side b, but usually has to charge it a bit. Din's Fire can actually 'cancel' his side b, forcing him to use tornado/up b earlier. Luigi's don't always sweet spot the edge either during tornado, so if you notice he has a habit of going slightly above the edge, you should try and punish with upsmash, up air, or even up tilt.
Don't let his jab shanninigans overwhelm you. You can shield his jab to prevent you from getting up b'd, though he may try and grab you. When you shield his jab, see if you can either do something quick OoS or spot dodge/roll away.