Where should I read?
Good books to start on are Matthew, Mark and Luke. Some books of the Bible are not generally suitable for this kind of reading, but are better suited to a more concentrated type of Bible study (see below). In the Old Testament, all the books from Genesis to Proverbs are fairly straightforward, apart from Exodus 21-40, Leviticus, Numbers, Deuteronomy and Job. In the New Testament: the Gospels, Acts, and the shorter Epistles are most suitable.
If you are studying a book in your church, (maybe the pastor is preaching though it or you are studying it in Sunday School), then it is a good idea to read the book devotionally yourself. You will probably complete it much faster than they will in church, but having read it, you will better understand what the pastor is talking about, and so get much more blessing from the messages.
What should I use to write in?
I find that the ideal notebook is about 6" by 4". Avoid getting one with larger pages or you will feel obliged to fill it each day, and it could easily become a burden. The problem with a diary is that when you miss a couple of days you can be tempted to try to catch up and fill the blank pages. It then becomes a burden and a chore. Experiment to find whatever suits you best.
Unless you have a very strong attachment to the KJV, you will probably get more benefit from a good modern version. I personally use the ESV.
Is this the only Bible Study I need to do?
No, this is the minimum. It is a good idea to set aside a block of time from time to time for the purpose of a more in-depth Bible study. Here you can study books that are not suitable for devotional reading. Problem verses that have come up in your regular reading can be looked at in more detail. For this kind of study it will help to have a concordance, a Bible atlas, and a commentary, as well as a good Bible dictionary. Dont be afraid to ask other Christians about problem verses, it can lead to some really beneficial discussions.