A veg garden on a slope can be done, and quite successfully. How difficult is going to depend on how steep the slope is, but even gentle grades will be easier if you plan on some cross-wise terracing. Do a small bit at a time, and it won't be overwhelming. Plan on paper first, then use flour or lime to "sketch" your plans on the ground! Always consider mature plant sizes [especially of trees and shrubs] and outline those as well. It's much easier to wash away flour than it is to dig up a 8' bush :-) Don't forget that both gardens and people will change over the years - but it's more difficult to change the hardscape, so try to keep stone, brick, and concrete-work basic rather than extensive. However, do plan on comfortable seating, whether it's a level spot for a couple of lawn chairs, or making some or all of the bed-walls with wide flat top-edges for sitting while you work.

Determine what material you want to use for the veggie bed "walls", keeping in mind that cost will need to balance durability; too cheap and you will be replacing too often; too expensive and you'll go broke quickly. I find a reasonable median is to use either cinder blocks or pavers. As is, the blocks are ugly, but they can be easily covered with hypertufa for a stucco appearance, with or without stone or mosiac-work. Pavers come in many colors and sizes, are more expensive than blocks, but by using fasteners [see link for one type], can be more easily moved at a later date. Don't forget to allow paths of a very generous width (think wheelbarrow-wide minimum) between growing beds, and to gently zig-zag the path from top to bottom to help prevent wash-out in hard rain. Try to limit the wall height of each terrace to under 18", even if that means a narrow bed. Over 18", and you will need to learn about drainage issues with retaining walls (not complicated, but potentially expensive). Permit yourself some bushes and perennials, especially along the edge of the lot, to soften the visual line - rectangular beds might be easier to use, but nature and your eyes will appreciate swooping curves. You might find using blueberries, lingonberries, and highbush cranberry along the lot-line and at the ends of the beds will add to your gardening pleasure. If you can, make one area near the top into a butterfly garden -- there is an exquisite pleasure in eating the season's first ripe tomato while watching the swallowtails flutter.

Learn about 'lasagna' for making soil and - If you haven't already- get a copy of Batholomew's "Square Foot Gardening" for best info on how to plant and maintain a good veggie garden. He recommends 4'x8' beds, but I find it easier to use 3x6 or 3x9 beds, and you may find some other measurement better. For convenience's sake, try to keep all the veg beds the same size so that you can easily interchange nets, etc. You don't mention trees, but you may want at least one -- put into a corner, it will provide you with welcome shade in the summer. Figure it's mature width, and keep the beds well outside that number -- else the tree will snitch the water and nutrients from your vegs.

Here is a link that might be useful: raised bed paver supports