Use helm-M-x and which-key, and avoid anything but use-package and customize. You don't have to eat the muscle-memory elephant all at once.
I've been using emacs for over 10 years and had zero issues with making the transition. On the contrary, it's simplified my emacs life quite a bit. The only thing I have not been able to get working is `eaf`, but that's clearly not the fault of spacemacs.