Need advice on a situation...

I have a potential client who wants me to be on call 24/7 as his virtual personal assistant. He's in the entertainment industry with musician's, actors and sports figures as clients. He's local but travel's a lot and has stated that he would require that I travel wiith him on occassion. We've discussed my role as an independent business owner and he clearly understands I would not be an employee. He actually prefers this vs hiring an employee. Based on the conversations we've had I know he will be a very high maintenance client but I'm used to that from my years supporting VPs, CEO's and Corporate Presidents. I'm considering taking him on as a client for the following reasons:
1. money is great - his retainer alone could support me
2. I'm single and used to being completely mobile/virtual with cell phone, iPhone, mini computer, web access anywhere with web card
3. I love to travel

My problem: I don't think I can keep my current clients if I take on this new one. I've toyed with the idea of hiring a subcontractor but my clients were all referrals and I'm not sure if they'll go for being supported by someone they don't know.

Any suggestions on how to have this conversation with current clients?

All feedback is welcome.

Thank you

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Portia Goss
www.thevirtualofficesuite.com