If this is your first time refinishing floors, you’re probably better off hiring a professional. Not only will your floors look better and last longer, but they will be finished much faster if you hire a professional. You’ll also want to consider the value of your time vs the small amount of savings you’ll gain by doing this yourself. If you’re looking to save money you may be able to do that by moving the furniture, ripping up the carpet/staples yourself, and buying the polyurethane and stain yourself (try Walmart or Amazon).
There are some real risks and downsides if you attempt to refinish your own floors. Most novices sand the floors too deep and therefore shorten the life of their hardwood floors. Skilled professionals know how to avoid this. If you sand unevenly, you can create divots and dips in the floor, and these can be permanent. Even if you hire a professional later, the weight from the machine will follow the profile of the floor. Pine and/or older or softer wood floors are more susceptible to sloppy sandings, so be extra careful if your home was built before the 1920s.
Regardless, be sure to throw away all the materials safely. Keep bags of saw dust containing chemicals least 12 ft away from the house. The sawdust can spontaneously catch fire, especially in hot weather.