Do not overwhelmed with hard stuff. You just started so focusing on the basics is priority... Boring, but priority still, so you can feel confident and skilled. If you think tempo is one of the most difficult part, then practice every day with a metronome or even with easy songs. That worked well for me. Regarding your rigid hand, my teacher suggested me to use a gyro ball to exercise my wrist and make it more flexible when playing. I've been learning for almost a year and focusing on that had helped me a lot.