1. Comfy saddle is really up what you prefer. You might try getting a saddle cover with cushioning instead of investing in a new saddle. It’s very dependent on what kind of cycling you are going to do.
Most of all get a good pair of bike shorts. No matter what saddle you’re on good bike shorts helps make every ride more comfy.
2. Put on your gear and tell yourself you’ll just ride for 10 mins – you’ll always ride for more.
Commit to a regular ride with a group.
Have someone take you to work with your bike. That way you have to bike home
3. You need to be carful with used shoes as they can be funky for all sorts of weird reasons. I wouldn’t buy a shoe without trying it on and seeing how it feels. In the short term you try getting straps for your pedal as an interim choice.
I’d suggest taking the plunge and buying new shoes and pedals. It’s really worth the investment if you’re going to be using your bike alot. They are also totally not necessary I rode a century ride before I got pedals.