There’s nothing wrong with using leaded solder, you just need to wash your hands after soldering. Many of the components made before RoHS will contain lead too.

Old capacitors may be no good. Electrolytic capacitors go bad with age. You can measure the leakage and ESR to see if they are still good. Any paper capacitors are going to be very leaky by now. If there are any oil filled capacitors from the 1970’s or earlier, they may contain PCB oil, which is very toxic.