Hi everyone! I'm a beginning meditator, and this is my first post 
Welcome to the forums Decadey

I've started learning meditation by reading several books on the subject, but got quite confused throughout the process. The first one was I think "Mindfulness in plain English", which advocated doing a Vipassana meditation with concentration on the breath.
Reading lots of books about meditation can make it a bit confusing. Especially as there are so many methods and schools and even philosophies that lay behind them. Henepola is a good author. I have one major disagreement with his teachings - I don't suggest concentrating on the area around the nose - this idea comes mainly from a mis-translation of the Pali though some people seem to find it works for them - which is an important part of meditation - finding out for yourself what really works for you.
The concentration on breath is not Vipassana but Shamatha meditation which is about relaxing your bodymind gently but in an awake and aware fashion, developing calm and concentration that lead to "one-pointed mind" or "access concentration".
Shamatha and Vipassana are like the two sides of a Möbius strip - if you don't know what that is, it's a one sided three dimensional object made by taking a strip of paper, half twisting it and joining the ends - Shamatha and Vipassana are both practiced simultaneously at all stages of meditation, though the School I learned from puts emphasis on Shamatha first and Vipassana as a fruit of Shamatha practice. Vipassana as you know means "insight" and it's much easier to have "insight" - see inside - when you are calm, concentrated, yet awake and alert.
Then I read "Deep Meditation", which was about mantra meditations.
Mantra is akin to a hypnotic effect. I am not convinced it helps deep awakening to the nature of reality.
Some other book suggested using the willpower to kick all the thoughts out of the head
Willpower used this way is just another form of thinking. You might successfully shut your mind up but you'll do so at a great cost - little progress.
...are these all just different types of meditation?
As I have written above, yes .. and no.
And if yes, then what is the best one? Or what is the best one to begin with? How do I determine it?
There is an introductory article on the frontpage you can find it here:
http://www.vipassanaforum.net/forum/index.php/page,10.htmlThis introduces Shamatha meditation. Mindfulness/meditation is a state of mind. Many people here have found this technique a powerful place to start their practice. Remember what you do on the cushion is called "practice" for a reason. That reason is that one aims to maintain mindfulness throughout one's everyday life, interactions with others, what you are doing moment to moment .. etc.
Also, should I meditate using the same meditation all the time or switch between different ones?
Stick to a single practice for a while. Develop that practice and the fruits that come from it. Mixing and matching tends to lead to confusion. Relaxed awake living is much more easily attained with a consistent practice.
Another question is about sitting - I can't currently do a full lotus, and a half lotus is quite uncomfortable - should I go for a simpler sitting position or should I exercise myself to be able to maintain the hard ones?
Have a look at the previous threads on posture in the
FAQ Here.
And finally (sorry for lots of questions
), do I understand it right that the final purpose of meditation is achieving complete awareness of the current moment and getting detached from your thoughts and emotions - i.e. you can experience them, but in a controlled process, as opposed to random outbursts of good and bad ones?
As you practice your thoughts and emotions will undergo many stages of change and flux. For now I would not propose you worry too much about any goal or final attainment other than starting to de-confuse yourself by getting a regular practice routine going and finding harmony in your day to day living (without this practice means nothing).
Hope that helps.
Warmly,
Matthew