This is not an uncommon problem.
I do not recommend outsourcing at this stage. A marketing exec should be the point person on your price point, sales distribution, CRM, sales staff and product updates, as well as direct public advertising/marketing/PR. It's an important position, and a qualified individual is frankly a necessary component to a successful launch. This is not someone who should report to anyone but you. That person will need good compensation, but there are always people who are open to a low(ish) salary with the possibility of a high payoff. Make sure you find someone with the right experience in companies that offered somewhat similar products, or at least companies that had good marketing in the same field. This person should be able to locate and manage sales and marketing staff as your company expands. You can look to outside companies later on, when you need fresh ideas for ad campaigns for new products and new venues.
As for determining the success of your marketing staff, a good analytical sales evaluation system will identify your most profitable customers, give you early warning data on your product's shortcomings, and of course identify and develop the markets most open to your products, current and future. This is the best you can hope for. There is no accurate way that I know of to determine in advance the performance of a marketing campaign for a brand new product. Once you have some experience you can make projections on new products and new markets (other countries, for example), but that will, hopefully, come later.
Good luck!
