In PRO-battles without MU Emerald works better against thunder of course, but its protection from Twins and Railgun is indeed not necessary, not very useful or remarkable. Therefore I'd suggest you to skip Emerald and go for Prodigi. I've got Emerald in my garage and the last time I used it was more than 6 months ago. ;)
Ricochet is notoriously common used at your rank and it's still being used commonly at higher ranks. Therefore some good protection paint is comfortable. If you rank up twice, you're able to buy Dragon which has 28% protection against ricochet, however I recommend you not to spend to many crystals to paints now. Achieve higher ranks and buy better paints then. The paints that unlock at low ranks are not useful anymore at higher ranks. As for Hammer, some protection is welcome, but it's not necessary in my opinion. Vulcan is more dangerous.