>>2972116In really low light, you might have some trouble, but for vacation photos, don't worry too much about turning your ISO up to 1600 or 3200. As far as other lenses to pick up, you could do worse than the 35mm f/1.8G. It could be a little longer than you really want, if you're trying to do a lot of extremely wide-angle shots on your trip, but it's overall a good low-light lens for crop-sensor DSLRs. Plus it is a cheap and lightweight lens.
And it's really hard to do any worse than OK with current DSLRs from the major manufacturers. For stuff like vacation photos, the D5300 should be just fine. Use it as much as you can before your trip, and get used to the button layout and menus. The last thing you want to spend your time in Spain doing is trying to figure out how to change your camera settings.
>>2972117Looks like it's f/3.5-5.6, depending on what focal length you're at.
