A weight belt from the barn? Don't use it. BCDs these days are weight integrated.
Some rental gear may have been ridden hard and put away wet.
There are two good sources for used equipment.
ScubaBoard.com classifieds
Facebook Scuba swap & shop group
Link
Regulators will need to be serviced before you dive them.
For BCDs you can test yourself if they hold air (orally inflate and see if they hold air for a couple of hours)
Think about what kind of diving you want to do. If you're going to be doing cold water diving you'll need a sealed first stage.
I prefer a plain analog pressure gauge and a wrist computer. You can pick up used computers for $150-$200. A Suunto Zoop/Mares Puck can do nitrox and would work for you for a while unless you want to get into tech diving.
Having the plain SPG and a wrist computer rather than a console does mean you need a separate compass. Consoles with computers do seem to go pretty cheap.