Hi guys, I'm pretty new to the world of bikes so please excuse my ignorance! I have a 1980s banana railegh bike without the rear wheel. I have a new wheel and I have just ordered a new 700 x 25 tyre. I now have to buy a cassette and chain but I'm clueless as to what exactly I have to look for.. I know the bike had a 6 speed cassette before but is it ok if I buy a 7 speed one instead? Thanks for the help!