I personally also run a small business from home and have a mixture of both personal and business traffic on my network. I have used many devices through the years and the only one so far which has fulfilled everything I have needed to use is a Netgear DGFV338 which is a business class (lifetime warranty) device which will enable you to connect through either PPOE or PPOA services and allow you to separate both types of traffic, provide wireless for your visitors without them being able to access your precious network. The device also had a decent firewall and incorporates VPN facilities if required.

I now recommend them to most of my clients who are in similar situations as you describe.

I hope this helps.