To be fair, I find users who simply come to a thread and instead of helping only derail the topic by being rude, worse than being ignorant.
Being ignorant or new at something is understandable, having knowledge and not sharing yet criticise who doesn't, isn't.
Anyway, Rydian already explained everything you needed to know, the DSTwo won't brick your 3DS, and your R4 Revolution probably won't work, unless it's one of the few R4i cards that work, out of those the best one would be the R4i Gold 3DS imho, but they only play DS and the emulators the DS scene has like GBC, Genesis, NES and SNES (although I think it's better to forget about the last one).