Reading

First of all it’s amazing that you are willing to skip to level that means you have confidence in your own abilities. I would suggest giving the N4 level, you just need to concentrate and work hard on the level you’re aiming to give. So consider studying a bit daily and trying doing different topics each day like kanji, then one day do a chapter of grammar, vocabulary, reading and listening (divide the work-trust me it makes it easy to remember then) Also remember to give mock tests at the end they are the best ways to know where your lacking and the areas you need to work harder on. Apart from learning remember to take breaks once in a while (I still struggle with this one) with all the knowledge you cramp it you need to remember to take breaks and have fun as it leads to better retention. 

I would give N4 a try before going to N3, since reading can be sometimes challenging in N3 if you are unlucky. This way you'll become familiar with the registration and exam structure and times allocated for each part of the test, and also elaborate your own strategies (like starting with the part you struggle with the most and leave the easiest part for last) About 漢字, it is indeed daunting at first (I personally love it!) take your time and start with the basics, you will learn soon enough that many of the more complex ones are a mix of different kanjis, this way you will find ways to remember the most complex ones. Remember to learn the correct writing order of the kanjis, this is not often considered in tests but in the long run it will make studying and looking for the characters much easier.

Don't worry, just keep going