I am at the very early stages of studying RE photography as a second career. My plan is to start off by shooting lower end homes while I study to acquire the knowledge and skill for shooting higher end homes. So how important it is to start off using strobes and flashes or can I just get away with using HDR in the beginning?
It's not essential to start off using small flashes. The method I recommend is to shoot brackets (3 to 5 frames separated by a stop or so) and then process the brackets with LR/Enfuse. It's a donationware Lightroom plugin that works on Mac or PC. It creates a good natural looking result. Technically this is called Enfuse rather than HDR but many call it HDR. The point is that LR/Enfuse works better for real estate than Photomatix which is a plugin that does HDR (tone mapping).
A great way to learn the whole process is Simon Maxwell's book: Enfuse and Hand Blending in Photoshop For Real Estate Photography. As Simon goes into in the book, there are benefits to using a single bounce flash when shooting brackets but it is not essential.
Using the LR/Enfuse plugin assumes you have Lightroom. Lightroom is a basic tool that all real estate photographers should have. It is the ideal tool for doing post-processing quickly. Simon describes in the book how to process a whole shoot in batch mode from Lightroom and do the final touch up that is needed.