1. Dear Enya, to deal with your points in sequential order, once you have paid the Supplier for the goods, the supplier has no control over who you sell those goods to or for what purpose they are used for. The goods once yours can be sold to whoever you like online.
2. Regarding the distribution of leaflets, it is perfectly legal for you to distribute them near schools or tube stations. The only legal requirement here is that distribution does not give rise to a prosecution under the Litter Act.
3. Again once the books from Taiwan have been paid for, you are free to rent them in the UK. Here you need to consider your business model carefully as books rented have to be returned. So you need to decide if you want to take the risk that the rented books will not be returned. However, there is nothing to prevent you renting the books in law.
4. Legally speaking, you need to attribute all articles which you refer to in your online postings. This can take the nature of a footnote or a link to the website which contains the piece being quoted. The latter is much more usual. Be aware that a licence fee may be payable if you footnote. So a link to the website is preferable.