1. Fine as is. 2. You need more info to make it coherent. I.e. the warranty expires in one week. Or 'the warranty expires after 5000 miles' Review your uses for the present tense, that should cover it. Basically you can use it to talk about general truths / things that will happen in the future, among others.

Sleep is uncountable but hours are countable. This works with other nouns too, where you include units. I.e. How much bread do you need & how many loaves of bread do you need? I would use 'many' for the second response based on this rule, because hours of sleep are countable.

Sure, but it depends on the language. There are a lot of resources for learning English online so you can probably have a reasonable go at it yourself. It helps if you live in a place that speaks your target language. Myself, I didn't get much out of classes, I really had to put myself in a situation where I was forced to learn, so I moved and got a job in a kitchen where my target language was spoken, and that's how I found success in learning. Others really thrive in lessons, some pick things up just by playing video games (this actually works pretty well). There's tons of ways to learn languages, but typically lessons are a good way, and a teacher can even help you find resources so you can learn on your own. I've had students that just wanted a list of topics and some practice exercises and off they go. Everyone's different.

There's nothing in the sentences themselves that indicate they need to be in past perfect. You need context to know this. For example with #4 you could say 'Puja won a big prize' and that's perfectly correct. You use past perfect when there's another event I.e. Puja had won a big prize before he decided to leave the fair. In your sentences the other event, or interruption is implied, not stated. They're not very good examples for explaining how to use the past perfect. You could also use present perfect I.e. Pooja has won a big prize. The implication here is some sort of effect on the present moment. Perfect aspect can be hard to get coming from languages that don't have it. Message me if you're still not sure.

Which is referring to terms here and it means words in this context. So they are giving you a list of words and definitions (I'm assuming) and those take precendence in case of inconsistencies between the documents. I hope that simplifies things.