I just got my first bike.
It's a used 7-speed mountain bike called the "Schwinn Sidewinder".
The seller did say it needed a "light tune up" and while riding it, it did seem cranky/slow/weak.
Even the chains are rusty although I'm not sure if that matters much.
I plan to go to a "bicycle cooperative" near me that offers space/tools/parts and guidance to repair a bike YOURSELF at a low price. I guess it would be a good way for me to learn since I am completely new to bikes.

Other than normal repair I plan to add the following things to it :
>Lights
>Back rack for baskets/panniers/backpack
>(Possibly?) front rack
>Security (U-Lock + Chain + tracker)
>Electric conversion using info from endless-sphere.com

I plan to use it mainly to commute to
>work(1.3 miles away)
>college(18 miles away)
>some stores I go to for "business" (5 miles away).
But most likely I will use the train in combination to the bike for college, until I convert it.
I live in densely populated urban area with a lot of restaurants so I am also planning to do DoorDash/Instacart/Uber Eats part time. I have in fact seen a few individuals do so on bikes around town.
And also just for fun. It is very comfy to ride a bike in nature and I like some cardio.

Any advice?