dont know much about online payments, so appologies for any daft questions....
I was told that if I wanted to add an online payment functionality to a site that it wouldnt be secure ( or a good idea ) if my site had shared hosting, is this true?
also, if I were to use, say paypal would I still need a ssl certificate?
Even if you have a merchant account, you don't need your own certficate, not if you use a company that provides the secure payment page for you. The SSL certificate will be provided for that part of the process, although it can't hurt to have your own SSL for the rest of your checkout process.