1.) i dont use vpn. Why you need one anyway?
if you get "not available in your region" message, all you need is to change the site language to japanesse. Ah, this only work at r-18 site (dmm.co.jp) not the all age (dmm.com).
or just play android version, no region lock bullshit and run lot smoother than browser.
4.) there is 2 premium summon. Make sure you roll the revival one, its the one with Berenice on banner, most of old units are there.
The other premium summon is filled with new classes that might be hard for new player to use.
Rinne have pretty big range too
no, you need to buy stuff to get them