Is it okay if I use the SLR process to analyse what people studied, find gaps/areas not researched on and use the findings to justify why I'm researching on a certain topic.
Absolutely, the findings of a SR could help with identifying significant research gaps. However, keep in mind that SR are comprehensive by their very nature and can be time consuming. Best wishes.
It depends on what gap you are looking for. If it is a specific gap stemming from a narrowly focused research question, then yes a systematic review is what is needed.
If you do not have a specific research question and you want your literature search to help you find one, then a scoping review will serve that purpose. Scoping reviews provide a wider view of the literature.
The differences are in the scope of each review (and hence the search methodology) as the practicalities are nearly identical (minus the quality assessment of articles in the scoping review being optional).
Have a read at these for further info:
Article Systematic review or scoping review? Guidance for authors wh...
Article Understanding scoping reviews: Definition, purpose, and proc...
First, it is important to understand the difference between systematic review and systematic literature review. Some people use these terms interchangeably, but there is a difference. However, the terms literature review and systematic literature review can be interchanged.
The systematic review has predefined steps which include framing the question, systematically search, identify, critically appraise research studies, and then synthesize the findings, but in literature review or systematic literature review not all of these steps are followed and search strategy is not made explicit. To conduct the systematic review, there must be at least two people while a literature review might be performed by a single person. Also, the systematic review has a protocol that should be prepared before a systematic review is started and used as a guide to carry out the review.
Secondly, it depends on the gaps you want to fill in as @ Constantinos Mamais said. If you want to identify new practices, identify and scrutinize the conflicting results, confirm or disprove whether or not the current practice is based on relevant evidence then yes you are good to go with systematic review. But if you aim to identify the knowledge gaps, clarify any key concepts and determine the scope of the body of literature then undertake a scoping review. The research question is broadly defined in scoping review, but highly and narrowly focused in the systematic review.
Depending on your field of research, I suggest appropriately apply (a) theory to guide your systematic literature review process. This paper outlines four approaches for doing so: Article The application of theory in literature reviews – illustrate...
It is useful, and many people kick of their PhD through an systematic literature review paper, but sometimes an SLR becomes so much effort that it will bog down the rest of your PhD, particularly for well-researched topics. Keep your PhD papers focused so that this does not happen.