I find that F11 gives me a good sweet spot in my lens to work with and have a great DOF. Looking at the chart and using F11 and 18mm, the hyperfocal distance to focus on is 4.7 ft. This will put everything from 2.35 ft to infinity in acceptable focus. You do not have to get out a tape measure, just guess the distance. If you are close to 6 ft tall, holding the camera close to your eye and aiming at something close to your feet will be close enough. After you focus, you can hold the shutter 1/2 down and recompose or switch the lens to manual focus so it will not refocus when you shoot. Working with a tripod, switching to manual focus is the way to go.
When you talk about the View Finder being too small are you talking about the back screen or the view finder you look through? Are you using live view to compose your shots. If so, I would only do this while using a tripod. Hand holding the camera away from your body like a point and shoot is not good holding technique and will lead to hand shake. I do not find the screen to be much help in the field because of the light. Using it to view the histograms will give good information on your exposure and seem to show up better in the light.
Good luck with your new hobby, it is one you can enjoy all of your life.
Jerry Jaynes Great Smoky Mountains of North Carolina