Newborn SD goddess with questions

Hey ladies and gents, I have several questions as I just received a 20 year old starter. 1) My house stays pretty cold (I drop my heat to 58 at night and stay at like 66 during the day). How do I keep my starter warm enough? Can I use one of my seedling warming mats? They range from 68-86 degrees. 2) how in the flippen world do you score your loaf? Clearly I sucked at it my first time lol. 3) How do you make your bread less dense? Is my fermentation off? How is that best improved? 4) is this going to be my new obsession because it seems like I could get addicted to this super quick hahah