Hahaha, don't worry too much about the Houston temps (since they are generally the same as Team Sugar Land) it will never get cold enough here to worry about the temps. I used to put my Hottop in stamped down snow (in Canada) and take it up to pre-heat temps of approx 170 and drop the beans in, I could see when things were getting to pre-heat temps based on the radius of melted snow. ;-)
If it got below -20 I would still roast outside and would just choose a windless day and add a few more degrees of pre-heat. I've found wind affected things more than temps, once things get a bit cooler outside. If I needed beans and it was a windy Canadian winter day I would roast in the garage. I've roasted in temps below -40.
As for filters, for the top filter I don't track it by number of roasts, I just look at it top-down while the roaster is roasting and if I can see the roasting element through obvious gaps in the filter material then I reorder a new one, I'd say they last for approx 100 roasts. For the rear filter the Scottish blood in my stretches the life cycle out on that bad boy for A LOT of roasts, once I see an obvious build up of residue on the filter material I boil some water, put a little bit of Cafiza on a deep plate, pour the water on the Cafiza, mix it up and then rest the entire rear filter assembly in the Cafiza'd water. I agitate the water a bit to help release some of the particulates and a couple of minutes later I take the assembly out and use a low pressure jet spray from the sink to get rid of the dirty water - be sure to use really, really low pressure or you will tear the black filter material. Set the whole thing outside in the sun to dry. Wallah, an almost eternally lasting rear filter.