At the moment addresses are used as fairly ephemeral things and the recommendation is to use a new receiving address for each payment. This limits the utility of vanity addresses and so I don't believe it's worth implementing. This may change in future however as new bitcoin services arise.
It can be implemented securely but the method touches on some issues I should currently keep confidential. However it's an elementary problem for any half-way decent cryptographer.
Indeed. I spent a while thinking about it and realized I was being stupid. The number of times the point was added initially (the private key) is unknown but you can keep adding it more without difficulty and get additional keys, then just add that value to the private key.