LOL You do have a lot of questions
There are so many techniques, opinions and articles here on BYC and the web about treating coops for lice/mites, I wouldn't know where to start. You may want to look at some of the popular bloggers like Chicken Chicken, Tilly's Nest and Fresh Eggs Daily for useful articles on the subject. Some use permethrin based products to regularly treat the coop, while others use herbs and essential oils. (Some don't use anything).
Personally I haven't had to treat my coop (yet

) it's always a possibility. I do try to shop vac the dust and cobwebs about every 3months, I also do sprinkle a very small amount of poultry dust (permethrin) into the bedding about once a month and mix some into the nesting material when I think about it. I add a small amount of wood ash to the run in various places, especially favorite bathing spots. So far, I have not had any problems, but my flock does take a dust bath about every other day.
As for heating in the winter...if you are going through summer months now, then of course you don't need the extra heat. By the time winter rolls around, it you don't start providing supplemental heat, the chickens should adapt to cooling temps and you won't have to provide any. I'm not sure where you are located, but even in the middle of winter here in N.C. (nights in the teens(F) I had a few that were practically naked due to late molting - they did just fine. I made sure they were roosting between a couple of girls. What you want to make sure of is they don't have direct drafts in the winter (air/wind blowing on them). You DO need ventilation though - so make sure their is plenty of venting above them to pull out ammonia from poop and to bring in fresh air.
For the roosting bars, I don't know the dimensions. If you ask over on the coop forums I sure someone would have some great ideas.
https://www.backyardchickens.com/forums/coop-run-design-construction-maintenance.9/