It sounds like things are mostly going very well for you - which is great!
With time, you will develop more confidence and figure out ways to get some of your personal time back. There will always be times during a projects where it will take a lot out of you, but you need to figure out a way to keep some guitar and definitely exercise going, even if it's minimal cardio.
I'm currently in an cool, but odd, situation to where I have 2 job offers with the potential for a third offer (all different companies) before I begin the first. I've already know my preferred option, but the onboarding process could take a while (several months and there are other potential risks ) and the other wants me to start in 2 weeks. I've been unemployed for over 10 months, constantly applying, networking etc.
So until I have a definitive start date at company 2, I plan on starting at company 1. I have to get back to work more for sanity than financial reasons.