Visiting for 5 Months

Hi I am a British citizen.

I would like to visit China, and study Chinese and martial arts for 2 months, and the remaining three months, I will be travelling as a tourist.

I will be doing this as a long period of travel around Asia. So although I have potential tentative dates in mind, I can not provide certainties of exact dates, but can be close to within a few weeks.

I would like to know what type of visa do I need to apply?
If I should apply from the UK, or whilst I am travelling abroad? I will be in countries such as Singapore, Indonesia, Hong Kong etc.

What do I need to provide in order to attain the visa?

I appreciate your help.

Many thanks.