If you're thinking about getting into running, I'd say the first piece of gear to buy is a good pair of shoes from your local running store. Don't worry about fancy watches or gels or arm sleeves or whatever.
I did finally buy a smartwatch (coros) last year, after training my whole life with just a casio. It's made me a lot more adventurous as having the GPS tracking means I can run offroad and even off-trail without worrying about keeping accurate track of my distances and paces. This is probably the second piece of gear I'd recommend buying and I wish I had done it sooner. The numbers are useful, it makes it easier to do the hobby, and it means I can use Strava which is a fun way to stay in touch with my fitness friends.
Third piece of unsolicited advice is that you absolutely don't have to run marathons.
> t. slow, but ran the fastest mile of my life last year, good friends with many semi pros.