ATMs are virtually everywhere, with almost all accepting Visa (Stanbic's taking MasterCard and Maestro). Exchange bureaus are found in most major towns.
Tipping is not common in chop houses or cheap eateries, but is more expected in upscale venues (a tip of 10% to 15% should suffice). Porters or bag handlers at the airport and bus stations will often expect or ask for a tip. A cedi or two should be fine.