Since you live close to a materials supplier the "only buy the materials you need for the next step" plan makes good sense. I also whole heartedly agree with practicing until you get proficient before tackling the real thing. Trying to teach yourself a new skill can be unnecessarily challenging. Having a teacher teach the the correct techniques, observe your efforts, and provide corrective suggestions can greatly speed your learning process and is usually well worth the cost in avoiding frustration and materials spent practicing. I live close to a medium size city that has a Makers Space that teaches welding, machining, and woodworking among many other topics. In addition to teaching they have space available for projects and many tools and equipment available that would normally be out of reach for a hobbyist. If you don't have a Makers Space near you I would investigate if your nearest community college or vocational tech school offers classes. There is an EAA chapter about 45 minutes from me that has space at the local air field where people build airplanes. Finding and visiting local EAA chapters and talking to the members to find out if any of them is or has built an ultralight, Light Sport Aircraft or Experimental Armature Built aircraft could also be really useful. They may know people who can provide training and access to equipment or build space. They can also be a great resource when you have questions, need a helping hand, or just some words of encouragement.
I too am nearing retirement and know I will need a project to keep from going crazy. I am a hang glider pilot but I've wanted to also fly powered ultralights too. My first step is actually to investigate getting my Sport Pilots License first to make sure I both have the appropriate skills and enjoy powered flight too. So far all my research has been via the internet so has only cost me time, but soon I will need to visit flight schools, meet instructors and start spending money on flight training, space rental for building, and hopefully, eventually a place to fly and store my creation. Like you plan to, I'm going to take it one step at a time.