to get your dwarves able to embark with it, you'll need to do one of two things. either make the coffee grow underground with something like [BIOME:SUBTERRANEAN_WATER] [UNDERGROUND_DEPTH:1:3] (snagged from pump helmets) or give your dwarves the tag [OUTDOOR_FARMING]. the first one doesn't exactly suit the way we grow coffee, and the latter doesn't exactly suit the dwarves themselves, if you want them to stick to only starting with indoor crops. if you give them outdoor farming, they'll embark with prickle berry seeds, wild strawberry seeds, and more, too.
you could just leave the plant like prickleberries and wild strawberries. grow outdoors, your dwarves will find them when asked to harvest plants in the appropriate biomes, and then be able to use the seeds (after the first batch are brewed) to grow outdoor farm plots. the [BIOME:NOT_FREEZING] tag means your herbalist dwarves will be able to potentially find it anywhere but tundra or glacier areas
as for what raw to put it into, you most likely want to create a new one, titled something like plant_mine, plant_more, plant_ random or the like. just to remind yourself that it's not from df itself, and needs to be moved over when they update. when you do this, make sure you say *something* in that file before the plant raws. the easiest to do is just copy the name of the file, so the first text in it says plant_more (for example), then the next line after that will read [OBJECT:PLANT] and then you can put your coffee plant a line or two below that (if this is confusing, peek at how any of the mods such as legend of forlorn realms, genesis, direforged, civilization forge post their unique plants and copy the style, they all do the same thing with the first few lines)