It's just as tough as getting all characters as mild spender. I missed 6 5*s (including Shenhe, whom I won't be rolling for) so far and my only non-standard character with constellations is C1 Hu Tao. I'd need to have won almost every 50/50 in order to get all characters, but well, I lost all but 1. Sure, I have 3 5* weapons and I got them within like 100 wishes in total, but those 100 wishes would have gotten me another Diluc constellation, so duh. But if I summed all the wishes up, they would probably give more than a single C6/R5 character. So, about a year of light spending and farming.