Could you elaborate more as to what aspect of the game is troubling you atm?. Hard to give you advice if we dont know if you want to improve Pvp, War, Events or Tournaments.
As for your emblem question. As a rule of thumb is never really worth it to invest on your 8th 4* node (if you are not going all the way to +18/or is a Key Event hero like Proteus). The increase is to much for the benefits imho, you are better off taking those emblems into another 4* or focus on 5*. As for moving them over to Santa, you are only getting 3 extra nodes if you reset her and you are not even using him as a Tank for your Wars, so I’ll say to not do it. +8 Xiu will do her job on War and can help on x3 Stacks also. That gives you a lot more benefits than a +3 extra node on your Santa (the extra % on his class ability is neat, but still not worth it atm).
Edit: If Santa was your Go-to tank or a Sniper Hero, then we could have a different argument about the value of those extra 3 nodes.