First off, I’m glad you like the website.
I think it’s great that you’re looking long term. Being so new to running, you can look forward to many years of improvements.
As for how much is too much, you know already what I’m going to state is the bottom line. Let your body guide you. I would strongly suggest not thinking about the numbers. As Zeke pointed out, it’s very easy to lay out these great plans and then end up throwing them in the trash because your body doesn’t work the way we usually lay out plans. At one point, you may be ready for a rapid increase. Once you make it, you may be “stuck” for a month or so before your body adapts and is ready for another increase. Base building is best done without a plan because it’s impossible to schedule your body’s responses. Maybe 140 mpw is possible, maybe 100 mpw isn’t possible.
As for what you are better off doing, why not a little of both? Base build through the spring and into the summer, going as high as your body will allow during that time, then pick a goal race in the fall and work on speed as you near that. I think it’s a mistake to ignore any component of training for high performance running, whether it be base, strength, speed, or anything else, for too long.
As for personal experiences, what has worked best for me has been incremental increases. One season, maybe I establish a 50 mpw base. Next season, I establish a 55 mpw base. The following season, maybe 60 or 65 mpw. The gradual process of incrementally increasing my training while also learning about myself all the time so I could train smarter and simply running consistently has really been the key to my consistent improvement over the years. Aim for consistent improvements over many years and you will look back 10 years from now and be astounded by how far you have come. As an example, in 2002, I ran a marathon into a 30 mph headwind at about the same pace per mile as I could run for 2 miles in perfect conditions in 1992.