You should be able to distinguish between materials for which permission is necessary and materials that can be used without obtaining permission. In general, consent is required for the reproduction of any material unless the principle of fair use is applied thus allowing the material to be used without permission. The relaxation for ‘fair use’ or ‘fair deal’ guarantees that copyright laws do not infringe upon your freedom of making a critical commentary on a work or using the work for teaching or research purposes. Examples of permitted use of texts under fair use are teaching, learning, criticisms, comments, reporting, and research. However, proper in-text citation and listing of sources must be done following standard practices.
Yes. Proper citation should be provided. If you are using more than 5 words in a row verbatim make sure to use double quotes and cite page number, as per standards
I think you can on condition that you provide enough information about the documentation of the quoted material. You may use direct quotations or any other paraphrased material in a similar way to the reference of original publication. There is no need to take the permission of the author since the article you take your information from has already been published.
You should be able to distinguish between materials for which permission is necessary and materials that can be used without obtaining permission. In general, consent is required for the reproduction of any material unless the principle of fair use is applied thus allowing the material to be used without permission. The relaxation for ‘fair use’ or ‘fair deal’ guarantees that copyright laws do not infringe upon your freedom of making a critical commentary on a work or using the work for teaching or research purposes. Examples of permitted use of texts under fair use are teaching, learning, criticisms, comments, reporting, and research. However, proper in-text citation and listing of sources must be done following standard practices.
Generally, yes you definitely can do that but in certain cases, it is better to seek a consent and permission from either the author (s)' or the Journal to do that. Most importantly, before citing any work, it would be better to read that work carefully to make sure that it really needs to be cited or not. As you may already know, some scholar kept citing scholars' work who are close friends, just to increase their google scholar index not because of the work really needs to be cited. This is just my personal opinion.
I'd say that the direct citing on published articles is allowed. Publishing an article, especially when you use open-access system, means you give authority to others who work on the same field with you to cite it whenever needed. In the author's shoe, citing his/her publication means as appreciation. Of course, there is special case where you will need the consent from the author/publisher. But in general, it should not have any problem to do direct citing on published papers.