Wherever you are comfortable and at ease with yourself is your home, regardless where you were born or brought up.('Home is where you lay your head' and 'Home is where you hang your hat' are also used.)
Someone who rules or controls something with an iron fist is in absolute control and tolerates no dissent. An iron fist in a velvet glove is used to describe someone who appears soft on the outside, but underneath is very hard.
'Mailed fist' is an alternative form.
If you jump in feet first, you approach a task or activity with little to no hesitation. When you jump into a swimming pool, there's no going back once your feet leave the ground- you will enter the water. When you jump in feet first with a new activity or task or requirement, you give it your best, knowing there is no going back.