welcome to srp

as far as brush from antique store goes, it depends. if it looks good i'd say it's very likely to work very well too. for cleaning it you can use shampoo.
as far as straight razors remember that whatever you get in an antique shop will need to be honed (about 99.3% chance) and you may not be able to spot serious issues with it because you don't know what these are. but it's fun if you don't mind loosing whatever you pay for it.
DE razors are easier to buy as they are just holders for the blades, so there really aren't much functional issues that you can't notice.