Hi Lydia!
Well, "וכך הלאה"/"וכן הלאה" - they are pretty much the same. they are pronnounced : vecakh hal'aa, and vekhen hal'aa respectively... the exact translation would be "and so on".
וכו' is a short version of וכולי, so it's the same. it has 2 possible pronounciations: vekhuley\vekhule (I think the proper way is the left one, but it does'nt really matter...). the exact translation would be "et cetera"
וכדומה is pronounced like this: vekhadome. I don't think it has an exact translation to english, but you use it when for example, instead of mentioning several things which are the same, you mention the first two, and then you say "vekhadome". for example: "I have many furnitures in my house. I have a table, a chair, a sofa "vekadome"
Hope I helped,
Aviel