Hello hardboiled, congrates on your purchase and welcome to the family.
I don't think there's much harm in leaving your UV filter on for nightshoots and indoors. If you picked it up as a kit, there's no doubt they would have given you the cheapest, possibly uncoated version of the filter, so there's a slightly greater chance of flaring, eg. when you shoot a nightscape with street lamps in the frame. But night shots are hardly optimal for image quality anyways.
The absolute purists will tell you there's potential for degradation of image quality with the two extra air to glass surfaces you just created by having a filter at the front of the lens - but on a zoom like the 18-70DX with in excess of a dozen elements, one more probably won't make that much difference.
For protection of the lens' front element and improvement of image quality, you should stick the hood on at all times except when using the built-in flash.