Welcome to Luigi boards! First off, you should look at the stickys first or go through the Q&A discussion
Here's a matchup discussion, a extensive post on MK should help cover what you need.
http://www.smashboards.com/showthread.php?t=174824
Here's a post of mine i just copy and pasted from my Q&A discussion
I haven't fought any good kirbys yet but I do know some a thing or two about Kirby.
Kirby has a great aerial game almost relatively equal to Luigi's and has a great ground game as well. Throwing a shorthop fireballs and some grounded fireballs can pressure Kirby and forcing him to approach you. Also a SH fireball to a tornado is a great racking up damage as well as utilts.
Fighting kirby can be abit tricky espically if they like to abuse the inhale. You must approach carefully when their near the edge because they can inhale you, drop down and spit you out underthe stage where you can't possibly recover or they'll just suicide.
Also Kirby's pretty lightweight and Luigi has alot of killing power against Kirby espically with his shoryuken. It kills Kirby around 41% so that's pretty early. Watch out for Kirby's Fsmash and hammar as they can kill and have decent range
Sparked's post
Approaching him: Might as well use the Fireball/Tornado Approach; this is if the Kirby isn't Final Cutter happy, if he is then Aerial approach him.
Kirby is an aerial monster much like Luigi, his FAir can't be Air Dodged for the whole duration and his BAir is much like your BAir, except your BAir slightly outranges Kirby to a small amount. Use it.
Don't stay on the ground too much. Kirby's FSmash lunges forward and has a deceptive hitbox... maybe it's not as deceptive as Pound, but eh. DThrow into FAir/BAir=>UAir. Keep him above or behind you. The occasional NAir will screw up momentum for Kirby.
DO NOT LET HIM COPY YOUR ABILITY; Heck, don't even let him inhale you. He's a lot better at spamming your Fireballs because they can be shorthopped AND puffed. You don't need that hassle. Dodge Final Cutter and the projectile if necessary and Punish with a FIRE PUNCH (If you're close enough!) Or a grab or an FSmash.
Don't even try to edgeguard him. If you're gonna try, try a DAir Spike; you might get lucky and KO him off the side instead.
Basically an even match because Kirby can't sue some of his combos on you, but it's harder to fight him aerially because of his multi jump attribute.