Did anyone, e.g., work the in Ostia but live east of the city and take a horse or ferry to work and back? Was it typical for some Romans to spend a few hours commuting every day, or was the shopkeeper-living-above-his-shop the norm, or both?

In a word, no. The daily commute to work is a thoroughly modern phenomenon. It certainly did not exist in antiquity, where there were no hourly jobs or steady wages. The majority of urban inhabitants were dirt-poor day laborers who had to find work on a daily basis and hope that the wage they were paid for that day's work was enough to feed themselves and pay for their rent, which was often paid daily, resulting in a semi-homeless population that floated around the city daily searching for work. The most privileged among the urban poor owned shops, which is really a shorthand for skilled craftsmen and shopowners, a relatively small subset of urban laborers. Neither shopkeepers nor day laborers would have traveled, except however far in the city a day laborer might need to go until he found someone willing to pay him. The extra money needed to afford daily travel into and out if the city was an impossible luxury, to say nothing of a horse, which was the mark of the supremely wealthy! Seasonally rural and suburban inhabitants might trek into the city to seek employment at the monumental building projects or at the emporium, but this was not a commute, they just became temporary urban dwellers for the season (or sometimes permanently). Nor did the wealthy commute--the wealthy did not have daily jobs (and senators were prohibited from doing any business, though many did anyway) to go to in the city. Either they maintained their rural estates (and went on tours if their various properties in the summer) or they lived in the city--every senator had at least one urban residence, the magnificence of which lent a lot of influence to the individual.

For leisure, how far (or for how long) would a Roman be willing to travel

He didn't, at least not often for leisure. The Roman laborer didn't get days off, unless he didn't get work that day or was lucky enough to own a shop that he could afford to close for a day (usually for political reasons). The urban worker didn't leave the city for short periods of time--if he was going to leave he was leaving for some time (or going home, if he was in the city for seasonal work). Within the city the urban inhabitant might travel some distance just to find an employer for the day, but if you've ever been to Rome you'll find its not really too hard to get from one end of the ancient city to the other. If he missed a day's labor he might hang around the forum or the Campus Martius, maybe making trouble if we're talking about the Republic--in the Principate measures were taken to try to ensure more of the population got work every day, and the emperors tried to keep the urban plebs busy as much as possible when they couldn't work. Besides work and political action people often moved around the city to participate in associative meetings like those of collegia, although these were often in neighborhoods, or to meet patrons--a huge swarm of people walked down to the forum every morning, many of them in the attendance of their patrons as they went to conduct public business. But I'd stress that we really don't know how much time most people had on their hands. It seems unlikely that the vast majority of day laborers had time to even really eat--food and money was always a problem for the urban poor (and their wages were, compared with the high cost of living, truly miserable--poor families probably had to be working all the time just to survive)--but for the privileged skilled workers there may have been the opportunity for some real leisure. He, of course, traveled around the city on foot--vehicles were rare in the city (and expressly prohibited in the day by Caesar) and litters were the privilege of the wealthy. But it's pretty easy to get around the city on foot