Welcome and congrats on your furbaby
#1 I never used a heating pad for Georgie and he didn't get cold trust me they will snuggle close enough to you to get your body heat.
#2 They normally stand up on their own some never due and boy are they cutie pies
#3 6 weeks is way too young they should stay with their mother until 12 weeks. Just keep an eye on him and make sure he eats and plays etc. notice any changes take him to the vet I wouldn't wait. Not trying to make you paranoid but they are so small it's better to take precautions. Oh and nutrical they love it and it helps keep their glucose levels normal.
Again welcome to YT Georgie is my first Yorkie and this place has been awesome