My advice would be to not worry about how you're ranking, especially because you're new. I have 553 Stamina, level 91. Could be a lot higher, but I'm sitting on 200 Peronamin and 250 Half Peronamin because....hoarding? Anyway, what I'm trying to say is you shouldn't sweat about falling behind, because you need to level up and get higher max stamina...leveling is a bit of a grind but it's necessary, and part of what this game is. Also, during the 2nd half more slayers will become available, and they provide an even bigger multiplier than the ones in the first half, keep in mind you can get free slayers in the N Gacha.

But yeah, like Tenhou said, you also need to figure out what's right for you. Personally, I was playing ALL Nutaku games and then it started to feel like busywork, so I quit all but Pero and have been perfectly happy since. Does Pero feel like busywork? If so, maybe that's an indication to quit.

In this event I'm approximately rank 150, will probably rank within the top 100 by the end and so far have spent 300 Gold on event gacha tickets. I didn't actually need to spend any $$$ because of the tickets I had saved up, but I usually buy the daily 100 Gold gacha ticket because I want the slayers for EVERY event. Now admittedly I have cleared the event gacha box (last year I did), and so now when a new event comes in, the only SRs put in the event box are the SR Slayers, so you're right, there is that paywall, but eventually you should be able to clear the box yourself, but it will be more a grind if you don't spend any $$$. My point being, I didn't have to spend any money to rank where I am now, but it certainly saved time from grinding and saving up items.