In principle, you can't bring RMB, but if you can find students from China there, you can exchange it from students from China. In general, you should bring foreign currency, not dollars. It is not cost-effective to exchange dollars for Cuba than to charge 10% exchange tax. You can take euros, pounds and Canadian dollars.

Consumption is higher than that of China, because Cuba is not an industrial country, and many industrial products have to be imported.

There is no limit to the quantity you can buy.