I feed mine usually 50% greens and 50% fruits and veggies. Greens include endive, mixed spring greens, collards, dandelion, clover (summer only), watercress, romaine, green leaf lettuce, celery leaves, kholrabi, raddichio, escarole, chinese cabbage, and kale. Kale should not be one of the staple greens as it can cause goiter if fed in excess. Fruits and veggies include prickly pear, pear, papaya, mango, watermelon, peaches, black grapes, plums, strawberries, blueberries, mandarin orange, butternut squash, spaghetti squash, pumpkin, zucchini, cucumber, pineapple, canteloupe, kiwi, dates, figs, green beans, peas, broccoli, mushrooms. The last four are fed very ocassionally for variety. For treats he also gets hibiscus flowers in the summer. Spinach has high oxalic acid levels which bind calcium so should not be fed often. I don't include it all in his diet, but a little won't hurt. Banana can be fed occassionally as a treat, but it is high in phosphorus so it also shouldn't be offered frequently.
I feed everyday, but don't worry if I miss a day here or there. Tortoises in the wild eat litttle bits all the time and walk around. That is why I offer food every day, and it is important to provide a large enclosure for the tortoise to get an adequate amount of excercise.
The enclosure needs to be high enough that the tortoise cannot make contact with the bulb. The type of lighting you use may dictate how tall your enclosure will be. I just use regular incandescent bulbs for my guy, but he does go outside during the summer so he does receive enough UV from that. My enclosure is 18" tall. All of those Repti-sun bulbs/tubes and the like are worthless in my opinion. A full 24 hours under a bulb is the equivalent to like 5 minutes in natural sunlight. Most don't give off UV past more than a foot away, in addition to which if there is any screen in front of it that significantly reduces the amount. Mercury vapour bulbs are a step up, but they are better suited to tortoise pens as I believe tortoises should be at least 30" from them. Redfoots have low UV requirements, they are most active for a short period of time in the morning in the wild and spend the rest of the day under cover.
Tortoises grow very slowly. I would recommend going with a medium sized enclosure instead of its full-sized adult enclosure in its earlier years.
Although tortoises aren't going to climb out of their pens, outdoor enclosures must also keep predators such as raccoons, cats, birds, etc out. Small tortoises especially are at risk for being picked up by birds.
The <a href="http://www.tortoisetrust.org">Tortoise Trust</a> has a lot of great articles and information you may find useful.