What is a reasonable target for converting fisrt page visitors to a sale or a lead

Depends on the nature of your site. I can share some stats with you:

On some of our sites we see a conversion as buying a product, and if the product IS SEASONAL OR TIMELY, we'll see up to 10% conversion on number of users to buying a product.

On sites where a conversion is sending an email (a qualified sales lead) we can see up to 15%.

Sometime a conversion is registering for a site in order to gain access to premium content. We can see up to 10% on a site such as this.

I know the banner click through rate is around 0.5-1%. That's a page impression conversion though, and there will be many more page impressions that unique users.

Hope that helped!