Use the structure in Farmer (this will work for most essay formats). 

Republican weaknesses = (i) political disunity (ii) military problems (iii) economic problems.

Nationalist Strengths = (i) political unity (ii) military strengths (iii) economic advantages (iv) Franco's leadership. 

Supplement your notes with Culpin and Henig e.g. nice quotation from George Orwell about divisions between the Republicans about how and why the war was being fought. Andrew Forest has a case-study essay about what the Republican defence of Madrid revealed about both republican strengths and weaknesses (56-61). On the strengths note the success of the propaganda and such legendary figures as La Pasionaria and the inspirational role of the International Brigades. On the weaknesses the lack of unity and political differences are well documented.