freelance writing-a few questions that i need answering

i have just finished my A levels and have been looking for part time work. i have been finding it very hard to find a part time job in my local area and so i was thinking about doing a bit of freelance writing for online companies. i have found a website that am considering https://www.odesk.com/info/uk/welcome/ and i have been writing my own blog for around a year now so i enjoy writing. my questions are:
what amount of time do you need to put into freelance writing?
whats the pay like?
what is the above website like for those who have tried it?
am i able to stop after the summer?
do freelancer's need to pay tax?