I live in an area that is inhabited with many do-it-yourselfers. They feel that they can do almost anything. Having done a great deal of work around my house myself, there are many things that can be done without professional assistance.
To the neighbor whose house was totaled by a fire that started in an addition that had not been permitted or inspected, or several other neighbors who have added things to their homes that were structural or required electrical or plumbing, I would strongly suggest that there are some things that should not be done without a professional. I would also strongly suggest that things that by law require a permit and an inspection need to be permitted and inspected. That is for your safety and the safety of the other people who live near you. There are, however, definitely some things that can be done yourself - even when a permit is required.
Although larger sites like commercial, multifamily housing and institutional sites require a licensed professional, most single family house sites can easily be designed and planted by the homeowner. This is due in part to the fact that larger sites require a minimum of a site layout of features like parking and walks, grading and drainage, storm water and nitrogen and planting to meet specific regulations. None of these things are usually needed with a single family residence, and the homeowner has as much training and experience in the endeavor of his personal site plan as most landscape designers / contractors or master gardeners. Also, with planting, there is not much that can really go wrong. The worst that can happen is that you will hit a utility line with a shovel or that your final outcome will look or function poorly. If this happens you might find that re-sale value drops a bit or curb appeal might suffer, but it is not something that would be extremely difficult to rework.
For people who plan to live in their home for awhile and want to do their plan and installations themselves, I say "Go for it." There are plenty of sources of information both in books and on the internet concerning the plant material that is available, and for a single family home, making a misplaced selection that results in an inappropriate choice or location is not a big deal. You might lose a few plants, but you will not be losing a forest. Play with it and do what will make you happy. If you want grass and like to mow, by all means plant it. If you like flowers and prefer to not to have to mow, plant flower mixes or make larger bedded areas or ground cover areas. If patio areas are your thing, make them.
Remember that this is your home, not your neighbor's, so do what will make you happy. Remember also though that there are laws that govern some aspects of land use. If you have a creek running through your property, for instance, care should be taken not to disturb or clear areas that might be designated for protection by the State or the Federal government. The surveyor who drew up your plat should be able to tell you if the water on your land is designated as 'blueline'. If so, you might want to consult a professional. Check your zoning and your local codes for any overlay districts as well. Some districts will restrict the amount of impervious surface area that they will allow. That could restrict the amount of paving you do or even the amount of structure you can build. Or it could alter the kind of paving to allow it to be pervious.
If you are planning to sell your house in a year or two, don't get caught up in adding a lot of stuff to make the house sell. Many people think that added features like a pool, a fire pit, or an outdoor kitchen will somehow help to sell the house. All too often these things add expense but are not wanted by the next guy who is not going to be willing to pay extra for them. Let the next guy add the features that make him happy. For a house that you will be leaving soon focus on making it look neat and well kept.
For most homeowners, who are really only looking to plant their site, do-it-yourself can be a very fun and rewarding choice. It will give you a chance to be outside and getting exercise. Keep in mind the local codes and ordinances and plant what makes you happy.