1) Taro wa itsumo uso bakkari (da). = Girls regularly drop the "da". 2) Mainichi shigoto bakari shite ite. = This sentence has an unfinished feel to it, which is deliberate, suggesting the speaker feels something toward it. Probably a little pissed off. 3) Kenka bakari shite irun desu = the "n desu" structure. I'm afraid you'll just have to learn that one. Additionally, not everything is about formal or informal. There are dozens of aspects in Japanese, and you can only learn them one by one.

1) It could be "Taro ha itsumo uso tsuite bakkari" as well. Uso is used as a noun here. 2) Shiteiru is the present continuous. There must be something following after this sentence. Otherwise, the sentence should be "mainichi shigoto bakari shite iru/imasu". "Te" functions to connect sentences. He/she is working all the time everyday, ... Mainichi shigoto bakari shite ite shinnpai desu. Mainichi shigoto bakari shite ite gohan wo taberu hima mo arimasen. 3) Shite iru here is also in the present continuous tense. It should be "... shite iru no desu." but we say "n" instead simply because it is easier to say, I guess. "Imasu" is the same but it is in the "masu" form while the first one is in the "desu" form. Hiroshi to dekakete irundesu/irunodesu/imasu. We even make it shorter to "shiterundesu", "dekaketerundesu", etc. as well.