Surface has a small screen and when you use regular Windows applications like Microsoft Word,Excel, etc, you may find it difficult to work especially when you are using touch interface. The apps downloaded from the Windows Apps store would work fine as they are optimized for touch.
You have an option to increase the font size and other display settings in Windows.
Select the Display and you will find some setting that will help you to increase the size of the fonts and display of apps
Here you can change the fond sizes and also you have an option to change the size of all items. I would suggest to go with the recommended settings but still if you want to make it larger, you can do so. You can also change the resolution if you want to try so, but again, you will lose the advantage of the colors.