It is entirely possible to travel around China hardly hearing any English at all. Tourist-industry employees across the land are more likely to speak English; in the big cities such as Shànghǎi, Běijīng and, of course, Hong Kong, English is more widely spoken and understood, but generally only among educated Chinese. In smaller towns and the countryside, English is often of little or no use: the vast majority of Chinese do not speak the language at all.
Learning Chinese in China is big business. Weigh up fees and syllabus carefully and check online reviews – some schools are pricey and may use teaching methods unsuited to Westerners. Consider where you would like to study: the Běijīng accent and setting has obvious cachet, but a course in a setting such as Yángshuò can be delightful.