If my issue with the Golem at the end of the Fiodh dungeon is anything to say, I don't know if soloing is totally possible (and I'm still in the Generation 1 story line!), but I've actually been keeping away from combat so far, so my knowledge is limited. There was actually an event recently that encouraged use of the various material gathering skills, so I haven't been in a dungeon or shadow mission in ages...

I know Mabi has a cash shop, but most of it seems to be either cosmetic or 'ease of use' style items. Now that do have gatcha stuff in rotation which I am less than excited about. So far, it seems like you can play the game and only run into the game pushing for the cash shop twice, in my experience. Once when you learn the style tab requires a key that only lasts for a month at a time, and when you go to change your appearance at Rebirth and find that some hairstyles and hair/eye colors are only available with Pon (their cash currency). The later I can forgive since you get some free Pon as a newbie, and I don't really change my appearance when going through rebirth, personally. But it is something worth noting, for those who are easily tempted by the shiny allure of cosmetics.