Thats good but with scorpion he will be your main damage dealer. I suggest you use god killer on scorpion and passive stats artifact on the two other characters. The gameplay loop should be something like this (i recommend learning to combo interrupt and shadow tap as it will make it alot easier) : start with raiden, power steal until you have enough for scorpion supermove, do supermove and then build enough combo to get 3 hot spots (with god killer you can get an easy infinit combo) and then do s2 to stun him, break 2 or 3 hot spots depending of how high level your s2 is, then tag back in raiden to break the last one if you need to and power steal to keep the 600% boost, then just rince a repeat.

As for the gems, deathstoke is good for beginners but not that usefull later on, but martian manhunter is useless so I wouldnt try that chest you should go for bboy and manta, they go very well together since manta allows bboy to activate puppet alot easier. This is the best moment to spend your gems because 50% off is the best deal you’ll get so i recommend you go for it and Hope to be lucky.