Some stuff I've learned from working on long-term projects:

Short-term goals are basically essential to any long-term ambition. If you have a really big project you are dedicated to getting done, try treating a chunk of the work like its own individual week-long project with an explicit beginning and end point.

I also think that its never too late to cut back on scope. Abandoning ideas can be a hard choice, but scope creep is very real and its really easy to accidentally become overwhelmed by your own ideas. Cutting back on scope never means the idea is gone forever, it just means curating them to make your project more currently feasible- you can always revisit it later once the most important stuff is done.