There aren't actually a lot of required licenses and/or credentials required for an accountant. However, if you need to be represented before the IRS in court, he or she must be an Enrolled Agent or CPA. For typical accounting work like tax prep. and reconciliations, etc., your accountant need only have a PTIN number from the IRS, which all accountants have to file taxes for clients.

I personally work with clients across the country and have used a lot of modern technology like Dropbox for secure collaboration. The key is having an accountant with a proven track record and have relevant experience for what you need. In terms of what exactly your needs, the more experience the better.