Think of your first build as practice before you build your dream. Maybe even think of it as the first of many 'practice builds'.
Get something that will take no more than 3 months to get on the road. After that, keep the down time for each new part of the build to 3 months. That way your less likely to become overwhelmed. In other words, don't do a complete tear down all at once - it'll stay that way, for years, sitting in the garage getting used as a shelf.
And realize, if you think it'll take 3 months, it will take 6. (If you think you can beat the system and plan for 6 months, it'll take 2 years
)