yes, the LCD will show what will appear on your pic, like any PNS. if you adjust shutter speed and/or aperture, or other settings like ISO, depending on your shooting mode, the camera will adjust accordingly. eg, if you are in Aperture mode, when you change the aperture on your manual lens, or change the ISO setting on your camera, it will adjust the shutter speed automatically to achieve the 'right exposure'.
As for keeping things in focus, 5N has two features that helps: focus peaking and touchscreen digital zoom. For focus peaking, you can just compose your pic on the LCD, and areas that are in focus will 'shimmer' with yellow colour (or red or white, depending on what color is preset by you). For touchscreen digital zoom, let's say you want to check whether a particular subject is in focus, you just touch the LCD screen where the object is shown, and the camera will do a 'digital zoom' or 'crop' that shows that particular area you touch only, so that you can adjust your focusing ring to make sure the details are in focus. Then, once you are happy, shoot. Or if you want to check composure again, half-depress to get out of the 'cropped image' to show the original image, re-compose, then shoot.
it's the perfect camera for manual lens. go youtube or browse thru the clubsnap forum, n u will learn more. Or even better, go down to the shop to try out.