New player's question about R, SR UR cards

Hi, I've been playing spirit stones for just about a week or two and the best card I can pull out is Seraz+ while making my way to lv 30, chapter 8. My team consists of the Seraz+ and the Rare+ I fused from 2 Normal+++ (Light Warrior+, Jen - from Quest - and Sword Dancer+). I've seen many others of lv 1x 2x with UR and lot of SR+ and I was kinda confused where did they get all of them. When I get on I often do the story quests and spend my Battle Stamina on Battles to get Emblems as collecting all of the emblems gives me chance of random boxes or rare cards, besides the weekly reward is decent as well. Ive read from somewhere that Hellgate is a better place to spend Battle Stamina on, and I tried to engage but all I get was hearts. I can barely fight lv1 or 2 monsters and it takes me 3 to 4 fights to finish them, how do we get the reward card anyway? I also tried to go through Devil Castle with free tickets but it's so hard even on easy mode, I think the farthest Ive reached was like stage 8 I still don't really know how those work, is there any other thing I can do to improve as a new player? Any kind of help or tip would be much appreciated! Thanks in advance!

Hellgate is not something you can do alone. Try only the easy bosses for now, and try to do them with friends. Alone it would be hard even with better cards than the ones you have.

Keep doing the free Devil's Castle every day, even if at first you won't be making much of a progress. To have more chances use hp equipment on all your quest party (attack is not as important as HP). You might even get a rare card you can use from wooden box eventually!

Try buying the 50k silver packs, if you have some extra gold. You might stand lucky and get an SR card.

You can improve your team by just doing quests. When finishing chapter 12 you get a SR card mage healer as a reward (phantom of aegis). It might not be as strong as seraz+ but the difference is not significant, so having aegis (since it's a healer) would be better than seraz. Also try to use BOTH the 'Heal All' spirit stones you will have by the end of the first continent!

After Brikeaz you enter Lysis. There you can get as rewards some R starter cards and if you defeat some of the ++ several times, you get SR boss cards!