What you can do is consider the cost and compare to the extra sales you could generate if some of your time was freed up.
You are absolutely right to be considering the option of a virtual office rather than committing to an expensive lease and hiring a full-time resource. Failing to maintain enough flexibility in your cost base during the early stages of your business is a common fatal error. This may prove more expensive in the short-term, but will provide you with valuable flexibility to scale up as your business grows.
The last point to consider is your credibility. In the early days you do need to work on credibility. The appearance of being large, stable dependable is important. An office and help is part of this. I on the whole would probably lean towards a virtual office so you can be free to pursue growth opportunities.
Extract taken from an article written by Brad Rosser who is a serial entrepreneur and former right-hand man of Richard Branson
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