First, I suggest you read about sequential explanatory designs in mixed methods research, which use follow-up qualitative interviews to help understand the results from a quantitative survey.

Next, you need to understand that structural equation models are only for quantitative data, so I suggest you do some reading on qualitative data analysis.

Your choice of analysis for the survey data is appropriate but using quantitative approaches to analyze the qualitative data from interviews is inappropriate. You can employ content, thematic, narrative, discourse, etc. analysis to the qual data based on your objectives.

What you need is a model. First, read a book or two on mixed methods. Creswell is a great place to start. Secondly, find dissertations in your program by others, so you know generally what your university expects. Thirdly, plan how your methodology will answer your research question, establishing delimitations upfront and forecasting limitations. The quantitative and qualitative methods will be different but complementary.

What Morgan calls sequential explanatory designs in mixed methods research, are actually two sequential studies that answer two types of interrelated questions, namely: general questions that are answered with quantitative strategies, and specific questions that are answered with qualitative strategies.

Researchers can choose a study method based on the formulation of the problem proposed. Just as an example, I once combined internet mediated research (IMR) strategies for general questions, and focused group discussions for specific questions. Of course, research subjects in the second stage of research (qualitative) were selected based on interesting findings from the first stage of research (quantitative).

In summary, as I have done, you can also modify the mixed research model offered by Creswell (2021).

I think the key thing about a sequential explanatory designs is that the follow-up qualitative methods addresses issues that were raised by the results from the earlier quantitative study. This direct connection is the source of the word "explanatory" in the name for the design.

Exactly correct. Different from conventional quantitative methods, explanatory sequential method researchers try to find explanations for the conclusions of the first stage (quantitative) research by interviewing (for example) subjects or actors. The focus of the second stage of research is not external causes as in the quantitative approach, but the internal reasons and intentions of the actors. This approach assumes that human behavior is discursive. Ask the subjects, why act like that?