Answer: You have an interesting project. You will need to consult with your local professional nursery staff who can provide more detailed suggested based on a better understanding of your planting site and your design goals. But here are some things to consider as you plan.
In your case, you will want to select plants that are usually low maintenance so they will look good continually with minimal care.
Since you have no easy way to water, you must select drought tolerant plants or install an automatic watering system or plan on spending significant time on hand watering when needed. I should point out that new plants will require regular watering while they become established. If they are not watered correctly at the beginning they will suffer root problems and may never grow well for you as a result, if they survive at all.
Based on your description I am unsure if you are planting into containers, oversized tree-scale boxes, and/or beds in the ground. This is an important distinction, in part because raised planters dry out faster than the ground, they are filled with a soil mix rather than than mineral soil, and also because they do not insulate the roots as well as being planted in the ground would do.
The next question would be at what part of the day the sun hits the area. Morning sun is much gentler than afternoon sun, for example. This will have a big influence on your plant selection.
Finally, is it windy? This can also have a strong influence on the plant selection.
Are there other special considerations such as de-icing salts spraying in from the street? Do you have a height limitation such as windows you must not block? And esthetically, are you thinking evergreens or deciduous, what color is the surrounding building and pavement? What types of plantings are nearby? To a certain extent you will want your plantings to blend in with the surroundings and complement your building or entry.
You will also need to have a more precise number up front for your budget. Budget considerations can be addressed in two ways, one is to purchase your preferred plant in a smaller/younger size and wait for it to grow, the other is to use a generally less expensive plant. Labor is a huge expense. You will have to budget for ongoing care and upkeep -- watering, annual top dressing of compost and fertilizer, mulching, weeding, pruning, spring and fall clean-up, and regular litter removal as stray things tend to accumulate in plantings.
As you explore the answers to the above types of questions, your best choices will become apparent. Your nursery staff should be able to help you analyze the growing conditions and identify plants that would thrive there, then you can select the ones you like best from those.
Enjoy your project!
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