Hello fellow tarantula owners

I recently purchased my first Goliath bird eater (Salem) I need a few tips for her tank weather I need to get a heat mat I’m currently waiting for my digital thermostat. My house usually stays at 74 but with colder weather coming I’m not quite sure if I need to get a heat mat or something else. Also any pointers on if Salem is a boy or girl I will update new pictures once the new enclosure is set up ( side note does anyone know a proper take size of a fully grown Goliath as of right now I have a 20 gallon) and also one more thing I notice that Salem has a leg missing is there a chance that he/she will grow back during mult not quite sure how old Salem is.