Hi Bgdog30, I just ran across your Phototron thread and I agree, whatever you are doing keep doing it; everything looks great from here. I have a Tron too. It wasn't free, $100.00 and a five hour road trip one way, but I am glad that I have one. Per you question: How often to replace the lights, if they are new bulbs then run them for three runs and check them to see if the color or intensity has changed. If not, run them for one more run. If not, take a look at HTG's website. They have bulbs that should fit your Tron that are made specifically for your Tron. I have a model that has pll or biax lights. They look like two fluorescents that have been welded at the top and join at the bottom that are connected with a four pin socket. It only has one top bulb though. Here are some pics of my current project. This is a Alien X Triangle that has been in flushing for a week now and hopefully ready for harvest within the week. I am not trying to invade your thread, just trying to give you an idea of what to expect. This is my inaugural grow too, so I am not very well versed in other growing methods concerning a Tron but if you dig around on the web obviously you should be able to find whatever you are looking for.
There is another member in this community of growers that did a thread on a Sour Cherry that she grew in a Tron that may be able to give you some advice if you need it. She had great luck with hers and swore by it. Anyway, sorry I have a tendency to babble, nice grow.
Best of luck to you