Below are some related previous questions with answers which might help too - but you need an Electrical contractor (your Search the List category) to determine your exisitng load, rating of the panel and service, and what effect the addition will have. Or if going to need runs through walls that will have to be opened up to install the wiring, possibly a Remodeling - General contractor to handle the electrical and repair/repainting work all in one contact.
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Generally speaking, unless you have some very heavy load circuits (like for a welder or large floor-mounted power tools say) or have basically an all-electric house, likely your existing box can handle it. If an all-electric house, especially if you also have electric hot water or space heating, maybe not - in that situation usually 150 or 200A service is needed. Breaker box may or may not have existing space for added circuit breakers even if the box itself is not up to rated capacity. Sometimes (depending on box design and capacity in use) you can replace an existing small-load breaker with a twin or half-width one which can handle two lighting or outlet circuits in the same space to free up space for the added circuits. Or if main service is adequate, sometimes you can upgrade the main breaker (if external to breaker box) and add a supplementary breaker panel direct off the service.
Get an electrical contractor or two in to give you a bid - could start with one and see if he is giving you a decent price for what you want, then if he says panel or service upgrade is needed also get a few more bids for that more expensive job if you decide to go ahead with it.
