Thomas' advice is sound - pick up a used Minolta 50mm F1.7 - supercheap, reliable, solid, and sharp - plus fast enough to use in low light situations. Places such as KEH sell them with guarantees and ratings - they might be worth a look.
As for ISO - use what works for you - everyone's sensitivity to noise is different - you'll hear some folks won't go over ISO400, some find ISO800 the limit, others comfortably shoot at 3200. It's all dependent on how much noise you mind or don't mind, and whether you use any tools to remove it a bit. ISO1600 might work fine in an 8x10 print, but cropping and viewing at 100% viewable size on your computer screen could look like a mess. So it really needs to be up to you to decide where the limit is. I had an A300, the forerunner to your camera, and was happy shooting to ISO1600 as long as I got the exposure right. I'd only use ISO3200 in emergencies.
Candlelight is very low - so you're still probably going to need fairly slow shutters, even with high ISO and with a wide-open aperture - if your subject is a person/portrait, advise them to sit nice and still until you tell them otherwise, and you might want to learn a good, steady grip, brace your elbows, and hold very carefully still while shooting handheld - the stabilization can allow you to handhold a shot up to 1/2 second or so if you're nice and steady, otherwise you may want to go with a tripod and turn the stabilization off. Either way, make sure you're shooting a static subject, or tell them to sit nice and still and not fidget around. If all else fails, light a few more candles and get a little more light on the scene!