Can you give some tips for a new player

So about 2 weeks ago i started dark souls 3 again after giving up on it 1 and a half years ago after getting to the castle after beating the first boss ( i didnt know what i was doing since it was my first souls game ). I dont really know what stats are best to upgrade or what weapons or armor is best. The weapon i use the most is the Estora ultra greatsword +6 with 314 dmg. Used the claymore before it and for armor i'm currently using the black night set with the sheild of want and the ring that boosts soul gains for slain enemies. Any good lighter armors? My weight is 76,8 even tho my vigor is at 22 and i'm fat rolling. And also any tips for pontif sulyvahn? He is kicking my ass good. Fought him like 15 times already. My estoria greatsword is doing good dmg with the carthus flame on it but i can only get 4 swings before i run out of stamina.and i almost got him once. 2 more hits and he was done but he got me with his clone double attack. Lost 26000 souls. So should i keep trying to end him or try something different