You are so much more qualified to answer your own question about meltdowns and discipline than i am, so take the following for what it's worth :)
My son has sensory issues that fuel his meltdowns, so the biggest thing that has helped those is OT and learning how to help him de-sensitise - but here are a few other things we do
First, I'm not fond of the time honored, 'just let them cry'. For a tantrum yes, but for a meltdown, well... i won't let someone else bite my son's arm until it bleeds why would I let him do it and just stand by?
If he was in a meltdown we just sit by and try to keep from hurting himself and have his'comfort devices' ready for when he breaks through. (his comfort devices include a bottle which he is too old for and only uses for comfort, but i'm good with it. he'll replace it with something else as he gets older, but it helps him break through and calm down it's worth it to me)
the best for us is avoiding them in the first place ... transitions are hard for evan, so we have pictures of the steps for an item - (i.e breakfast, turn TV off, dress, daycare)that we reference hundreds of times - it takes us 30-40 minutes to get dressed now in the morning or go to bed, because we keep referencing the pictures until his mind is ready to move to the next step - but we do it without meltdowns (usually). Routines are supposed to be great, but my job doesn't allow that, so this was the closest we could come.
If we're out in public, i talk him through it .. ok, at the store we're going to get these 5 items ....ok we have 4 of them, i just need you to stay in the cart until we get the other one, it's going to be 'milk' can you help me find it? what color of milk should we get today? .. it's an ongoing dialogue that i'm sure makes me look crazy, but it helps a lot. It also helps if i keep to my word, i can usually get by with saying, oh i forgot we need to get cereal too, let's stop here, but if i do that for more than one or two things we're in for it.
If you find any secret tricks, let me know!