Framework for Research Design

In Chapter 4, Robson puts forth five components of research design. These are:
Purpose: What is the study trying to achieve and why is it being done?
Theory: What theory will guide your study? What conceptual framework links the phenomena you are studying?
 Research questions: To what questions is the research geared to providing answers? What do you need to know to achieve the purposes of the study?
Methods: What techniques will you use to collect the data, and how will be it be analyzed and deemed to be trustworthy?
Sampling Strategy: From whom will you seek data? Where and when?

I will now attempt to answer these questions in order to put more order to my research design. 

Purpose: I would like to discover if foster kids are affected by socioeconomic factors (education and financial situations of their foster parents and biological parents) and/or constant displacement and/or age affects their reading/literacy and if this in turn affects going to the library.
Theory: This is the only part of the research design I'm not 100% sure of what they mean.
Research questions:  I would like to look at how their age may or may not affect whether the child reads or goes to the library, how the foster kid's backgrounds may or may not affect their literacy and whether or not they choose to visit the library, if their FP and/or bio parents encouraged reading or read to them, are they readers now and/or go to programs at the library - if no, what could the library do to encourage use?
Methods: I want to use questionnaire after I get parental permission (and possibly permission from foster care agency such as DSS), for the children and maybe even a separate questionnaire for the foster parents.
Sampling Strategy:  I would like to do the questionnaire with foster kids ages 5-18 (this age group may change) and possibly foster parents in my current county, maybe even at a particular agency to get a smaller sample group.