I mean, if you do boot covers then it probably doesn't matter. I say what I did because I use sacrificial shoes in my builds, which makes boots by far the most expensive part to build.
At the end of the day though, it's whatever works for you
Funny you mention shoes i found this post just today and damn if it wasnt an insight and a half 1st Build - WandererTJ's Mjolnir Mk. V (Custom) - S-128 - [Hybrid Build] [Pic Heavy]Always been a fan of the Halo: Reach Scout. Not enough out there. Well done!
Also, I am the exact opposite of RandomRanger . Id rather start at the boots for because there's so much room to hide crimes when learning. Plus it gives you that integral learning curve of how to properly reinforce seams and plan for high stress sections of armor. That and its fun to just have goofy over-sized shoes first before anything.
I also tend to start with helmets when I worked with clients, because at least if they don't know if they want to do a full suit, they still have a kickass display piece. I learned most of my painting tricks from working on them.