Should I look up every word while reading, and when to start RCs?

nope nope.. no need to do that beta.. you can fix some time, let's say 20 minutes everyday, before you are about to keep the book down. In this time window, you look up every single word, but apart from this, as long as the meaning of the sentence is clear to you, or the particular paragraph is clear to you, you can conveniently ignore the word and move on. Developing a healthy reading habits requires you to reading in a flow and most students begin to hate reading or books simply because they are asked to check dictionary every time a new word appears. The whole point of reading is to learn, understand and enjoy. As long as you are able to understanding the text, you can enjoy it and read in a flow. Learning will happen automatically when you are giving it enough time. Coming to the second half of your question, once your reading and comprehension is sorted, RCs don't take much time. 2-3 months are enough (including accuracy improvement and speed improvement), so you can focus on RCs in August or even in the first week of September. But remember, it's very important to sort out the other things before you begin solving RCs because if your reading habits are still poor or if you still find it boring to read things, no matter how many RCs you solve, you won't be able to go beyond 60-70% accuracy which will make average.