It is quite hard to give a precise answer to the question, how much does someone buy on margin? You would be able to calculate this yourself, using some spreadsheets and tables. On the other hand, you can hire an advisor who can do this for you, who has access to many investors with the same objectives as you. Even if you are an amateur in the field, this is one of the things that you need to be careful about, since your goal is to make money as quickly as possible. Also if you are not careful you can end up losing all of it.
Your aim is to buy a lot of Bitcoins and then sell them when the price goes above your margin requirements. Of course, you want to buy at a lower price than your margin requirements are. If you are new to the field, it might seem that there is no need to worry about this, but you should not underestimate the power of leverage. What do I mean by this? If you manage to get a large number of Bitcoins and manage to sell them at the right time, you could easily double your investment.
There are some people who buy a very small amount on margin, so they can safely start using this method without having to worry about losing all their money. This is probably the best way to start trading, especially if you have no experience. Then you will be able to learn more about this subject and hopefully make some money. If you manage to buy a large amount on margin, then it is probably not such a good idea to trade this way. You might find yourself in deep trouble.