The most definitive way to sex a snake is to take it to a somebody who knows how to do it and have it probed. Still not 100%, but it's the most reliable method. Make sure the person doing it is experienced and good at it, or you could end up with a damaged snake. Another method is to check the shed skin: A male sometimes leaves sperm plugs attached to the shed on the point it was attached to the cloaca (they look like little yellow horns), whereas a female just has a hole. That method isn't overly reliable though, so if you attempt to sex it that way then do so with a grain of salt. Unless you're planning on getting another to breed with some people never bother, but sometimes it's nice to know
Oh, and to answer your other question, there are several schools of thought on heating. Depending on the size/setup of your tank some people are happy with just a heat mat, some just a lamp. Others will go both (temperature regulated, usually via thermostat to avoid overheating), it's really up to you. In a smaller space just a mat or lamp would be fine; a mat would be more cost-effective electricity wise, as well as maintenance, as heat lamps can blow on a regular occasion and are usually relatively pricey to replace in the long run, but there have been some horror stories to do with heatmats and shorting out. We use heatchord under coreflute (sp?), which has proven to be quite adequate for our animals, as well as light on the pocket.
One really good purchase would be a temp gun, that way you can monitor temperatures yourself instead of relying solely on a thermostat or 'feel'. They're not too expensive, and not all electronics are 100% reliable, so you'd have that backup to a stat. It brings a certain peace of mind