In the first one, these expressions BOTH are used to mean that something is correct, or to confirm information. They can also express agreement if you're listening to someone else. For example: NOT YOU Says to you: "I hate driving during rush hour, it takes forever!" You can just say, "yeah, true," as in I also hate it too. Or, maybe you had brought up the subject earlier, and then they mentioned hating the traffic too. Sometimes people say "right?!" with a more excited tone.
In the case of correct information, both "that's right" and "that's true" are interchangeable. As for "yes, I got it/I understand," you can say "Alright." It may seem strange, but "alright" isn't often found in dictionaries because many people say it is WRONG, but everyone speaks and writes it that way. Normally you'll find "all right" in the dictionary.
For 2, most people say "from now... until (usually a time/event)." Alternatively, you could say, "I should search for the results of the tefl for now." This means that for the next chunk of your time, you'll be searching for tefl results. If you do something "from now on," it means that you're going to always do it in the future. For example: "I went to the store during it's posted time of business, but it was closed. I'm always going to call them in advance from now on"
Is there any plan to go abroad, or are there any plans to go abroad are both okay. Is there any plans to go abroad is technically wrong because your verb isn't in the plural form. Native speakers will often make this "mistake" when speaking quickly and starting a sentence with the word "is" and then they continue speaking anyway.
4: these can be interchangeable as well. I can also say, "I don't know which meal to order," or, "I don't know which country I would enjoy the most."
5: Would implies that you'd have to put yourself in the place with the feast. Maybe you're thinking about going. Will just says it as a fact. Yes, there will be a feast.