I really have to respond to these posts in case someone comes in here looking for advice and reads all this.
I'm big on accuracy and critiques since this is how I can help best, so apologies in advance if I possibly come across too harsh with my comments below. I know everyone is just chiming in and being helpful too! -^_^-
I find myself starting ground comboes either f-tilt or the dash attack...
F-tilt is for spacing (a quick 'knock-away' attack), not a combo-starter. If you want an example of a F-tilt combo lead, check out Sheik.
... f-throw after a dair+utilt+dair combo near the ledge...
D-air to U-tilt works great, especially if you're already facing away from the opponent when the D-air finishes. A second D-air won't 'combo' after the first U-tilt... just consider it's huge start-up requirement.
I can see a second D-air working if you expect that your opponent is bad enough to immediately Air Dodge into the ground after a low-percent U-tilt, though.
dair to multiple dtilts works pretty well...
This is viable and pretty safe. The damage output is pretty dismal... unless one of those D-tilts trips and allows you to combo/chase into something rewarding.
Fair so that only the first and second kicks...then use Dtilt which can lead into an Fsmash
...Fair first or second kick, then land into a turnaround Utilt > Dair > Utilt > whatever you really want...
Kirby doesn't have enough frame advantage after the second hit of the F-air, though if you read your opponent correctly, the D-tilt comes out quickly enough to beat out some slower attacks, such as Smashes and Grabs.
The first hit of the F-air is much better for a set-up, but it requires a LOT more precision to utilize.
Dair > U-tilt > Up-B
From here you can Uair juggle and end in a Fair
This sort of works up until you get to the Final Cutter which takes way too long to get a hitbox active (see above, regarding D-air). It's still viable as a mix-up to catch an opponent if they choose to react quickly thinking you're going to hit them with something fast... but then again, there are probably better options to use in such a situation.
Falling u-air -> u-tilt -> b-air -> falling u-air -> reset...
Congratulations, this is the most reliable and effective combos of the thread.
A fast-falling Up Air, though tricky to pull off on most characters, will lead nicely into a U-tilt. It also gives you the option to face away from the opponent to set Kirby up for a solid U-tilt, or to face toward your opponent when landing for a better chance at a weaker U-tilt (which is useful when the opponent has a bit of damage on them already). B-air is a nice finisher since it adds about 13% damage to the combo, is easy to pull off on all characters, and can shove the opponent off-stage where Kirby has a greater advantage.
The second Up Air is stretching the combo a bit... Kirby has to catch up to his opponent, jump, and then start Up Air. This gives the opponent way too much time to respond, though it does keep the pressure going, which allows for great mix-up opportunities to keep your opponent guessing. So the second Up Air is not entirely implausible... more like 'unlikely' or 'inconsistent'.
A good substitute for the B-air is either:
U-air, if you want to go for more pressure from under the opponent.
N-air, if you want to bring the opponent down closer to you.
No attack, if you think your opponent is mashing for an Air Dodge. Punish when they land with impunity.
Shield is also a good option if you think your opponent is mashing for an attack.
d tilt to f tilt to f smash is one at low percentage
D-tilt doesn't really combo into F-tilt unless it trips, but it's still a great follow-up because F-tilt has a quick start-up. You shouldn't get much out of the F-tilt though, but if the opponent is trying to press in on you immediately I can see another F-tilt working (you really shouldn't go for that F-smash due to the high probability of getting Shielded/Dodged and then punished badly).