About 20 minutes a day is plenty for a pup of 4 - 6 months old. By the time they reach maturity at about 1 year old increase the time spent walking to about an hour each day. However, some dogs have a very strong hunting instinct and may never be safe to let off. The secret is to start young and make it fun for them to come back. My Wire is very well behaved and obedient.
Wires have absolutely no road sense.
Your garden needs to be completely dog-proof, with a good fence all round. Make sure any gates are clearly marked so that visitors shut them properly. They can become persistent barkers so you do have to work hard with them as puppies to ensure they know when to be quiet. It depends on how good a coat your Wire has. Apart from stripping the coat 2 - 3 times a year, your pet wire will need a thorough brush and comb each week.